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Severe Tropical Cyclone Ian


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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

The first tropical cyclone of the South Pacific 2013-14 season has formed at around 19S, 175W, to the east of Fiji. Ian is a tightly wrapped but small system, with some deep convection and formative banding features. Winds are at 35kts. Shear is low over Ian, and waters warm along track. This should allow some intensification over the coming days, which could be rapid due to Ian's small size. The cyclone is currently heading southeast along the southwest side of a ridge to the northeast. This ridge is expected to lose influence of Ian in a day or so, and a ridge to the south is expected to turn Ian back towards the west. The timing of this turn is uncertain, and there is some spread in model guidance.

 

Ian is the first cyclone to form in Fiji'a area of responsibility of the South Pacific since Haley in February of last year.

 

post-1820-0-00937600-1388964308_thumb.jp

Edited by Somerset Squall
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Posted
  • Location: Eastbourne, East Sussex (work in Mid Sussex)
  • Location: Eastbourne, East Sussex (work in Mid Sussex)

Posted Image

 

Tropical Storm SEVEN: Probability of Cat 1 or above winds to 120 hours lead

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Tropical Cyclone Ian approaching Tonga

 

A tropical cyclone alert has been issued for Tonga as the first cyclone of the 2013-2014 South Pacific season approaches the country. Tropical Cyclone Ian is currently east of Fiji.  Fiji's Meterological Service says at midnight universal time the category one cyclone was intensifying and moving slowly, 270 kilometres north, north west of the Tongan capital Nuku'alofa.

 
The cyclone is expected to bring damaging gale force winds over the northern Ha'apai and Va'vau group of islands - about 300 kilometres north of the capital - where a gale force wind warning remains in place. Ian is packing winds of 75 kilometres per hour close to its centre, expected to increase to above 90 kilometres per hour as it intensifies.
 
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Posted
  • Location: Dursley
  • Weather Preferences: 4 seasons please
  • Location: Dursley

This does seem very late for the first of the season. My recollections 20 years ago when my parents lived in Samoa was that things were a lot livelier a lot earlier, usually around beginning of December. Also my limited understanding suggested a slight correlation between El Nino/La Nina and activity in the South Pacific area. Do you know whether there is any truth in this?

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Posted
  • Location: The Netherlands
  • Location: The Netherlands

This does seem very late for the first of the season. My recollections 20 years ago when my parents lived in Samoa was that things were a lot livelier a lot earlier, usually around beginning of December. Also my limited understanding suggested a slight correlation between El Nino/La Nina and activity in the South Pacific area. Do you know whether there is any truth in this?

 

According to NOAA, more tropical cyclones develop in the South Pacific ocean during an El Niño event. However, less tropical cyclones develop in te Australian Basin due to an El Niño event.

 

As stated from NOAA:

 

 

The Australian/Southwest Pacific shows a pronounced shift back and forth of tropical cyclone activity with fewer tropical cyclones between 145° and 165°E and more from 165°E eastward across the South Pacific during El Niño (warm ENSO) events. There is also a smaller tendency to have the tropical cyclones originate a bit closer to the equator. The opposite would be true in La Niña (cold ENSO) events. See papers by Nicholls (1979)Revell and Goulter (1986)Dong (1988), and Nicholls (1992).

http://www.aoml.noaa.gov/hrd/tcfaq/G2.html

 

Concluding, there does seem to be some correlation between El Niño events and TC activity.

 

Current state of Ian

 

Ian itself appears to be less organized than it was yesterday, as it lost its banding features. It consists mainly of a distorted blob of deep convection, while still covering the low level circulation center. Moreover, a visible imagery loop shows the convection moving westward. I don't know wheather this is because of TC motion or upper level shear.

 

Below a Dvorak image of Ian:

Posted Image

 

Ian is currently under weak southerly shear (about 10 knots), as analyzed by CIMSS. This is generally favorable for development, though the analysis above could suggest stronger eastern shear setting up over Ian.

 

Sea surface temperatures appear to be around 28*C, warm enough to support TC development (as seen below on the GFS track forecast and sst map).

Posted Image

 

However, the forecasted slow motion of Ian may cause upwelling of cool water and possibly weakening if the tropical cyclone stays in its spot for too long.

 

Track forecast of Ian

 

As seen above, Ian is forecast to move very slowly toward the west for the next 3 to 4 days, before curving back toward the south-southeast, as it is being picked up by a trough.

 

Because the UKMET and CMC models initialized the system only barely, they gave somewhat erroneous forecasts, and are not shown here.

 

The official forecast of the JTWC mainly agrees with the GFS solution, though the initial motion is a tad more to the south:

http://www.usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/warnings/sh0714.gif

Posted Image

Track forecast from JTWC

 

Overall, there seems to be reasonable agreement on the future track of Ian, though the quasi-stationary movement is usually very difficult to forecast. 

 

Intensity forecast of Ian

The JTWC forecast slowly intensifies the system up to 50 kt, and then shows very modest weakening in the latter half of the forecast due to shear being caused by an upper level trough to the south of Ian. Moreover, they expect Ian to keep a steady intensity in the short term, which seems reasonable given the current cloud pattern. The upwelling of cold water could be a complicating factor in the intensity forecast.

 

Sources:

http://tropic.ssec.wisc.edu/#

http://www.ssd.noaa.gov/PS/TROP/floaters/07P/07P_floater.html

http://moe.met.fsu.edu/cyclonephase/gfs/fcst/index.html

http://www.aoml.noaa.gov/hrd/tcfaq/G2.html

http://www.usno.navy.mil/JTWC/

Edited by Vorticity0123
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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

Interesting to note that Fiji Met brings Ian up to 75kts- certainly being much more aggressive than JTWC.

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Posted
  • Location: Dursley
  • Weather Preferences: 4 seasons please
  • Location: Dursley

Don't know how much historic data you have access to, would be curious to know how often it occurs for two strong cyclones to be side to side. Instance I am referring to is Cyclone Val and Cyclone Wasa in Dec 91. (A strong El Nino year I believe) Due to the dynamics of it, Western Samoa bore the full effects for 3 and a half days.

As for Ian, fairly small based on the info above.

Very interesting thread, so thanks to all for keeping it updated

Edited by noonoo418
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Posted
  • Location: The Netherlands
  • Location: The Netherlands

Interesting to note that Fiji Met brings Ian up to 75kts- certainly being much more aggressive than JTWC.

That is certainly rather agressive, considering the state Ian is currently in and its organizational history. Though conditions will remain seemingly favorable during the next few days (apart from possible upwelling).

 

By the way, the latest forecast from Fiji Meteorological Service only brings Ian up to 40 knots. That must have been a rather steep decrease in forecasted intensity. The graphical intensity forecast can be seen below:

Posted Image

FMS graphical forecast

 

Fiji meteorological service never brings the intensity above category 1 (wind speeds up to 53 knots1)

 

The JTWC forecast has been increased in intensity in the latter parts of the forecast, with winds up to 55 kt being maintained at the end of the forecast. Moreover, the forecast has also shifted the short-term forecasted motion more toward the northwest, to become more in line with the GFS. As a result, Ian will be crossing slightly higher SSTS (up to 30*C)

Posted Image

JTWC graphical forecast

 

Don't know how much historic data you have access to, would be curious to know how often it occurs for two strong cyclones to be side to side. Instance I am referring to is Cyclone Val and Cyclone Wasa in Dec 91. (A strong El Nino year I believe) Due to the dynamics of it, Western Samoa bore the full effects for 3 and a half days.

As for Ian, fairly small based on the info above.

Very interesting thread, so thanks to all for keeping it updated

That's rather impressive to have (multiple) tropical cyclone(s) impacting land for so long. But to answer your question, there were multiple occasions of interactions between strong tropical cyclones in the past. The last one that comes to my mind was in the West Pacific, with Parma and Melor interacting with each other in 2005. They were both major hurricanes at the moment of interaction.

 

Posted Image

The Fujiwara interaction between Parma and Melor in October 2009

 

About the frequency of such intense cyclones (in this case major) interacting with each other, I don't think it is a very common event, but I dont have access to any data for such interactions. It seems like it is something in the range of once every 5 years. 

 

And finally, (because I really like those images Posted Image ) a MIMIC TPW (based on water vapor) loop of the Southeastern Pacific, in which Ian is also clearly visible (the spinning red color on the map):

 

Posted Image

 

Source:

http://www.met.gov.fj/aifs_prods/20032.txt

1= http://en.wikipedia.org/wiki/Tropical_cyclone_scales

http://www.usno.navy.mil/JTWC/

http://tropic.ssec.wisc.edu/real-time/storm.php?&basin=seastpac&sname=07P&invest=NO&zoom=4&img=1&vars=11111000000000000000&loop=0

http://www.examiner.com/article/the-fujiwhara-effect-typhoon-parma-and-typhoon-melor

http://tropic.ssec.wisc.edu/real-time/mimic-tpw/ausf/main.html

Edited by Vorticity0123
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Posted
  • Location: Eastbourne, East Sussex (work in Mid Sussex)
  • Location: Eastbourne, East Sussex (work in Mid Sussex)

Tonga warning cancelled as Tropical Cyclone Ian veers towards Fiji

 

A tropical cyclone alert which was issued for Tonga as the first cyclone of the 2013-2014 South Pacific season, has now been cancelled. The Tonga Meteorological services cancelled the alert but said a strong wind warning remains in force for Ha'apai, Vava'u and the Niuas.

 
Ha'apai is about 135 kilometres north of the Tongan capital Nuku'alofa, while Vava'u is about 305 kilometres north of the capital. The heavy rain advisory will remain in force for waters west of Vava'u and the Niuas. Tropical cyclone Ian was located about 220 kilometres west of Vava'u at 10pm Monday with estimated winds of 40kt near its centre and momentary gusts of up to 55kt. "The cyclone is currently moving west at about 4kt away from Tonga," Tonga Meteorological services said.
 
Principal Scientific Officer with forecasting at the Fiji Bureau of Meteorology and regional Tropical Cyclone Centre Misaeli Funaki says it's now heading for Fiji, but isn't expected to make landfall there. "Over the next few hours we expect it to take a southward turn, and then it will gradually track towards the southeast away from Fiji," he said. Weather warnings have been issued for Fiji's outer islands.

 

 

http://au.news.yahoo.com/a/20624862/cyclone-warning-for-tonga-cancelled/

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Posted
  • Location: Dursley
  • Weather Preferences: 4 seasons please
  • Location: Dursley

I found this today, an interesting insight into what is being seen as an warmer than average year in the South Pacific

http://www.islandsbusiness.com/news/samoa/4134/pacific-posts-record-high-temperatures-in-2013/

 

Should more cyclone activity be anticipated due to warmer sea temperatures as suggested by this article? Only time will tell..... 

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Posted
  • Location: Eastbourne, East Sussex (work in Mid Sussex)
  • Location: Eastbourne, East Sussex (work in Mid Sussex)

GDACS Event Report - Summary

 

Posted Image

 

The image shows the total rainfall accumulation associated with the cyclone.
 
Tropical Cyclone IAN-14 can have a low humanitarian impact based on the Maximum sustained wind speed and the affected population and their vulnerability.
 
Updated: this report is based on advisory number 4.
 
Tropical Cyclone Tropical Storm (maximum wind speed of 101 km/h)
from 06/01/2014 06:00 UTC to 07/01/2014 06:00 UTC
Population affected by Category 1 (120 km/h) wind speeds or higher is 0
Vulnerability: Medium
Extreme Rain
Potential rainfall is calculated based on rainfall observed by several microwave satellite sensors.
 
Storm surge
 
The tropical cyclone did not reach sufficient strength to cause significant storm surge.

 

 

http://www.gdacs.org/report.aspx?eventid=42304&episodeid=4&eventtype=TC

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

Ian has finally started to strengthen. Winds are up to 45kts currently. Ian's satellite signature is much improved this evening, with the shapeless blob now morphing into wrapped convection. The steering environment has remained weak, but Ian has drifted northwards slowly. Further strengthening is likely for the next few days.

Edited by Somerset Squall
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Posted
  • Location: Eastbourne, East Sussex (work in Mid Sussex)
  • Location: Eastbourne, East Sussex (work in Mid Sussex)
Cat 2 - Tropical Cyclone Ian, threatens Niuafo‘ou
 
Wednesday, January 8, 2014 - 17:00
Nuku‘alofa, Tonga
Now upgraded to Category 2 storm in Tonga, Tropical Cyclone Ian is moving towards Tonga’s northernmost island, Niuafo‘ou, and on its current track, TC Ian may bring damaging gale force winds to Niuafo‘ou in the next 12 to 24 hours.
 
The Fua’amotu Tropical Cyclone Warning Centre stated at 4:00pm today that the intensifying TC Ian was 200km southwest of Niuafo‘ou at 1:00pm, when it was moving north. A gale warning remains in force for Vava‘u and Ha‘apai, while a strong wind warning remains in force for Niuatoputapu and Tafahi.
 
TC Ian has estimated winds of 50 knots near its centre with momentary gusts up to 65 knots.
 
“The cyclone has moved west at 5 knots in the last six hours and continues to intensify. The system is expected to become slow moving then turn and move southeast in the next 24 hours,†Fua‘amotu TCWC advised.
 
Tropical Cyclone Ian, that formed two days ago near the Vava‘u Group, was upgraded to a Category 2 storm overnight by the regional RSMC Nadi Tropical Cyclone Warning Centre on a track moving southeast across Tonga, between the Vava‘u and the Ha‘apai Groups over the next three days.
 
The Fua’amotu weather forecast for Tonga, issued at 4:00 pm November 8, 2014:
 
NIUAFO‘OU:
 
Northwest winds 15-20 knots increasing to 25 to 35 knots with momentary gusts of 35 to 45 knots in the next 12 to 24 hours. Rain developing heavy at times with flash flooding expected. Seas rough to very rough with moderate to heavy northwest swell.
 
VAVA‘U AND HA‘APAI GROUPS:
 
North to northeast winds 10-15 knots increasing to 20-25 knots with momentary gusts of 30 to 35 knots in the next 24 to 48 hours. Seas becoming rough with moderate northwest swells.
 
NIUATOPUTAPU and TAFAHI
 
Northwest winds 15-20 knots increasing 20-25 knots in the next 12 to 24 hours. Cloudy periods with occasional showers developing in to heavy rain. Seas becoming rough with moderate northwest swells.
 
TONGATAPU and ‘EUA:
 
Easterly winds 10-15 knots, mainly fine apart from cloudy periods with few showers, moderate seas with moderate easterly swells.

 

 

http://matangitonga.to/2014/01/08/cat-2-tropical-cyclone-ian-threatens-niuafo%E2%80%98ou

 

Posted Image

Tropical Storm IAN: Probability of Cat 1 or above winds to 120 hours lead

Posted Image

 

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Hey, so I've been reading up a lot about cyclones and such over the past couple days though it's still up in the air as to how much actually sunk in.

So my question is, what's causing Ian to make such a drastic about turn?

Also, (if this is the wrong place to ask this, just ignore it) if a low pressure forms on the west coast of South Africa for example, and it builds up decent wind speeds, what would need to happen to it before it would be considered a cyclone?

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Posted
  • Location: The Netherlands
  • Location: The Netherlands

Hey, so I've been reading up a lot about cyclones and such over the past couple days though it's still up in the air as to how much actually sunk in.

So my question is, what's causing Ian to make such a drastic about turn?

 

The main contributor to the forecasted corse change of Ian is a trough forecast to pass to the south of Ian in a couple of days, essentially reversing the steering winds around the tropical cyclone. The steering change can be seen below: (Sorry about the poor charts, but I unfortunately don't have access to better charts regarding steering mechanisms):

 

Posted Image

GFS T0h (06Z)

 

Ian is the 1000 mb low at the extreme western part of the map. For the steering influence, focus on the geopotential heights (colors) and not the surface level pressure (white lines).

 

Note that the geopotential heights always decrease when one moves from the equator to the pole, because there is generally colder air located at high latitudes. Within this colder air, lower pressure levels are being reached lower up the atmosphere. (for example, 500 hPa pressures at 70*S are located at 4000 meters altitude, and at 40*S at 5000 meters)

 

What can be seen is an increase in geopotential heights to the southeast of Ian, indicative of a high pressure area at higher altitude. The high pressure area blocks ian from moving toward the southeast. Moreover, because the high pressure area is not very close to Ian itself, the steering winds are generally very light.

 

Looking 66 hours later:

Posted Image

GFS T66h (06Z)

 

The blocking ridge to the southeast of Ian has dissipated. in contrast, at T66 lower geopotential heights can be seen extending northward toward Ian. This is indicative of a trough (or low pressure). What happens is that the steering flow around that trough basically captures Ian and recurves it southeastward.

 

In short, the drastic turn of Ian is mainly due to a high pressure area to its southeast dissipating and making place for a trough, which initiates a recurve scenario.

 

 

Also, (if this is the wrong place to ask this, just ignore it) if a low pressure forms on the west coast of South Africa for example, and it builds up decent wind speeds, what would need to happen to it before it would be considered a cyclone?

 

There are many characteristics of a tropical cyclone. For instance, a tropical cyclone needs to have at least a low level circulation center (this causes turning of the clouds). Moreover, it shouldn't have frontal characteristics. And there are many more. Some more characteristics are in the link below:

http://www.bom.gov.au/cyclone/about/

 

Interesting to note that Fiji Met brings Ian up to 75kts- certainly being much more aggressive than JTWC.

Well, it seems like a maximum intensity of 75 kt isn't as bad as it seemed to be 2 days ago! JTWC is also keying on 75 kt at the middle range of the forecast. Quite suprising!

Posted Image

Also interesting to note is that Ian is basically tracking forth, back and, if the forecast verifies, once again forth over the same piece of sea!

 

Visible imagery shows Ian is a very small cyclone, meaning it is susceptible to rapid changes in intensity. It also contains some banding features, and JTWC noted a mid-level eye feature. This means continued strengthening is most likely, concerning current signals.

 

Posted Image

 

It will be interesting to see how Ian will evolve during the next few days!

 

Source:

http://www.wetterzentrale.de/topkarten/fsavnwt.html

http://www.usno.navy.mil/JTWC/

http://www.ssd.noaa.gov/PS/TROP/floaters/07P/07P_floater.html

Edited by Vorticity0123
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Posted
  • Location: The Netherlands
  • Location: The Netherlands

While the UK is currently in the mood of cold weather, Ian has continued to intensify. Last visible imagery shows a weak eye feature assoicated with Ian. The compact cyclone now consists of a circular ball of convection with some banding features to its north and south.

 

Posted Image

 

Currently, the intensity 

 

During the last few days, forecasted intensities have been upped considerably, with top wind speeds up to 100 kt (major hurricane!) now forecast (as shown by CIMSS). Fiji Meteorological Center is indicating cat.4 intensity (on their own scale, this is equivalent with winds between 86 and 107 kt).

 

Posted Image

 

This once again shows that much can still be learned about those tropical cyclones, regarding intensity as well as track.

 

CIMSS ADT satellite estimates are currently at about 55 kt, but this might be related to the small size of the cyclone, possibly leading to underestimation of the intensity.

 

The track forecast has become much more certain, now a well-defined steering mechanism has developed (the trough to the south of Ian).

It looks like a few islands will be hit by the tropical cyclone, with much stronger winds than previously expected. However, as Ian is a small cyclone, a slight deviation in track could result in a major change in impact.

 

Finally, CIMSS MIMIC imagery of Ian. Such images nicely show the internal structure of tropical cyclones.

Posted Image

 

 

The loop is over 48 hours. Many structural changes can be seen in the loop, but the most important are the last few frames. They clearly show a circular eyewall developing, which could be an indicator of a burst of Rapid Intensification. It is very impressive to see a tropical cyclone evolving and organizing that quick. 

 

One thing that does make me wonder about such images is that most structural changes seem to be rather subtle. Does anybody know if there is any truth in that theory?

 

Sources:

http://tropic.ssec.wisc.edu/#

http://www.met.gov.fj/aifs_prods/65661.html

http://www.nhc.noaa.gov/

Edited by Vorticity0123
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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

Ian's winds are up to 60kts according to JTWC. But I agree Vorticity, Ian looks like it is undergoing rapid intensification. This, perhaps, shouldn't be all that surprising given Ian's small size and the drastic improvement in outflow Ian has experienced today. I expect that emerging eye will clear out very nicely soon.

 

post-1820-0-91008000-1389218689_thumb.jp

 

 

Edited by Somerset Squall
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Posted
  • Location: Eastbourne, East Sussex (work in Mid Sussex)
  • Location: Eastbourne, East Sussex (work in Mid Sussex)

Cyclone Ian picks up strength

 

A cyclone north of New Zealand was this evening declared to be a major storm threatening a large area of Tonga, home to 110,000 people.
 
Tonga's Meteorological Service warned tonight that Cyclone Ian had become a category four cyclone, one short of the most intense storm on the scale. Ian formed earlier this week as the summer season's first cyclone and had meandered around the Koro Sea - between Fiji and Tonga - without threatening settlements but has now gained strength. Its latest warning says the northern Vava'u group is facing the first hit from Ian while a gale warning is in force for the Ha'apai group.
 
"Tropical Cyclone Ian has estimated winds of 139 kph near its centre with momentary gusts of up to 176 kph." Ian is continuing to intensify and is now moving south east.The service warns flash flooding can be expected with seas becoming rough to very rough. Earlier today the US space agency Nasa released data from its Aqua satellite which showed powerful thunderstorms surrounding Ian's centre of circulation. "The strongest thunderstorms were concentrated around Ian's centre and in bands north and south of the centre where cloud-top temperatures exceeded minus 52 degrees Celsius," Nasa said. "Those thunderstorm cloud tops have cooled over the previous 24 hours, indicating that they're higher in the atmosphere and that Ian is strengthening."
 
Ian was centred about 500 kilometres east-northeast of Suva, Fiji. If Ian later this week heads off south into the Pacific, an 86-year-old sailing training ship Picton Castle could be in harms way. It took part in the Auckland Tall Ships Festival in December and left Opua on December 29. The ship, based in Nova Scotia, flies a Cook Islands flag and is heading for Rarotonga as part of a global voyage. This morning it gave its position as 41 degrees south, 163 degrees west and doing 13kmh. Crew on board this morning tweeted that they were watching the storm: "We've got our eye on it!"
 
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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

Ian has undergone a period of rapid intensficiation overnight. Winds are up to 85kts, cat 2 on the SS scale. Ian developed a well defined eye overnight, which has since become obscured by cloud. Ian has veered east also, and should turn south-southeastwards soon. For about another 36hrs, the environment supports some intensification. As Ian gains lattitude, waters cool, and shear also rises, which will initiate extratropical transition in a few days time.

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

Ian lost organisation this afternoon, with the eye no longer visible. However, Ian's eye has emerged again this evening, and the cloud pattern is tightly wrapped again as opposed to the rather shapeless blob of this afternoon. Winds have nudged upwards to 90kts. Ian should strengthen further over the next day or so as the cyclone heads south-southeast.

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Posted
  • Location: Eastbourne, East Sussex (work in Mid Sussex)
  • Location: Eastbourne, East Sussex (work in Mid Sussex)

Tonga in the path of destruction?

 

Cyclone Ian approaching Tonga with 'catastrophic' winds

 

Forecasters are warning that an increasingly powerful cyclone directly threatens Tonga's northern islands.

 

Forecasters in Fiji are warning that Severe Tropical Cyclone Ian is directly threatening Tonga's northern islands. In the latest advisory, Ian has been raised to a Category 4 system with average winds of 170 kilometres per hour and gusts of up to 230kph. It is moving slowly south east towards the Vava'u and Ha'apai groups and brushing below Niuafo'ou, Tonga's most northerly island, in the Niua group.
 
Leveni Aho is the Director of Tonga's National Emergency Management Office. He says Ian may continue to intensify. "The potential and the threat now lies in the islands of Vava'u and Ha'apai in the next 12 to 34 hours," he said. "We have been in contact with our northern islands, the weather still there is pretty calm but we expect that it will escalate." The key administrative island of Vava'u and its capital Neiafu - Tonga's second largest town - shares the same name as its group, while Lifuka island and its regional capital Pangai is the administrative centre of the Ha'apai group.
 
Destructive winds are likely to begin several hours before the cyclone's centre passes overhead or nearby Vava'u in the next 18-24 hours, and across Ha'apai on Friday afternoon local time. Heavy rain, the flooding of low lying areas and very rough seas are also expected. A forecaster from the Fiji Meteorological Service, Sanjay Prakash, told Radio Australia's Pacific Beat the cyclone will be "catastrophic" and "bring a lot of damage to the kingdom". "It will be at its peak during the time of landfall," he said.
 
Mr Aho is urging local residents to prepare for the worst.
 
"A reminder to people to make sure that they have enough supplies for the next 72 hours in terms of water, drinking water, and food and (ensure) some basic necessities like radios and mobile phones are charged to maintain communication," he said. "Make sure that they are in a safe place, if ever the winds arrive keeping away from low lying areas and the coastal areas, make sure that they are in a safe house, sheltered."
 
Earlier this week, a cyclone alert was issued for the island groups of Vava'u and Ha'apai with warnings of gale force winds, heavy rain, squally thunderstorms and the risk of sea flooding. The alert was cancelled early on Tuesday, but both the Fiji Meteorological Service and the Tonga Meteorological Service re-issued warnings on Wednesday. Ian has been hovering in the ocean between Fiji and Tonga since Monday.
 
Islands prepare 
 
People in Tonga's Vava'u islands have begun boarding up windows in preparation for Cyclone Ian. Kjelll Stayv owns a small hotel in Vava'u and told Pacific Beat there is an eerie feeling in the air. "The skying is milky and grey so there is definitely something coming," he said. He says preparations for the cyclone are underway. "On our island and the small outer islands here, there are between 10,000 to 12,000 people," he said. "And right now there are now many tourists, maybe 100. "It is a little weird because we have to board up their windows, but they don't have much choice I'm afraid."
 
Fiji-based climate advisor Neville Koop says preparations must be made under such a threat. "You need to be taking your preparations very seriously at this time (as) it does look like the damaging winds will start in Vava'u probably late tomorrow (Friday)," he said. "So that is some good news for people in Vava'u, in that they will have some daylight tomorrow to do some more preparations." The latest cyclone tracking map, issued by the Nadi Tropical Cyclone warning Centre in Fiji, predicts Ian will be weaken to a Category Three system in about 36 hours, further weakening to a Category Two system in about 72 hours.

 

 

 

http://www.radioaustralia.net.au/international/2014-01-09/cyclone-ian-approaching-tonga-with-catastrophic-winds/1245376

 

Tropical Cyclone IAN: Probability of Cat 1 or above winds to 120 hours lead

Posted Image

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Posted
  • Location: The Netherlands
  • Location: The Netherlands

It appears like Ian has become the first major hurricane of the 2013-2014 season in the SW Pacific! (Saffir Simpson Hurricane Scale). What a beuaty it has become!

 

Rapid intensification event and satellite presentation

 

Satellite imagery shows Ian now has a well-defined eye embedded in a nearly circular area of convection. This shows a burst of Rapid Intensification has occured during the last few hours. The visible imagery also beautifully shows the development of a clear eye, along with the RI.
 
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On the Dvorak image below, the well-developed structure of the cyclone can be readily seen with the nearly circular and intense ring of convection surrounding the well defined eye, typical for major hurricanes.

 

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CIMSS ADT intensity estimates also show the rapid intensification of Ian, though their estimates continually underestimate the strength of the cyclone. As noted previously, this may be due to the small size of the cyclone. I expect the intensity to be increased markedly within the next few hours.

 

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Size of Ian

 

The small size, as noted above, of the tropical cyclone can be seen below:

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This image is a Multiplatform Tropical Cyclone Surface Winds Analysis (MTCSWA). (an analysis of winds at the surface in cyclone Ian) This image is composed by integrating mulitple satellite intensity images near the surface1. The radius of tropical storm force winds is about 389 km2, which is pretty small for a major hurricane.

 

Another image showing the small size can be seen below:

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Given above is a satellite loop of the whole South Pacific Basin, with Ian located in the center-left of the image. Note how small the system actually is!

 

Environmental characteristics

 

Data from http://earth.nullschool.net/ shows two large inflow channels at surface level. One wide channel originates from the equatorial Pacific (to the northeast and northwest of Ian, as well as one small channel from the southeast. The wide equatorial channel consists mostly of warm, humid air, as well as the one to the south. However, there is a sharp air mass gradient near the southwestern inflow channel. Just to the west, there is a line of very dry air, as can be seen in the water vapor imagery below:

 

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Water vapor imagery of the South Pacific. Note the dry air (black) to the southwest and west of Ian.

 

As the line moves further eastward, the dry air could get entrained into the circulation of Ian. The result would be severe weakening of the system.

 

http://earth.nullschool.net also shows Ian has a well-defined polar outflow channel, which aid in the ventillation of the system. (check 250 hPa for upper outflow analysis). What can also be seen at the 250 hPa height, are very strong upper winds to the south of the cyclone. As Ian is forecast to move south as well, it will experience much increased shear values in a few days, due to these upper level winds.

 

All in all, Ian has proven to be a tenacious tropical cyclone! After hampering some in the beginning, it has become a formidable and beautiful system. Unfortunately, some islands are directly in the path of the major cyclone. Let's hope they stay safe!

 

Sources:

1http://www.ssd.noaa.gov/PS/TROP/MTCSWA_UM.pdf

http://tropic.ssec.wisc.edu/#

http://www.ssd.noaa.gov/PS/TROP/mtcswa.html?storm=SH072014&id=IAN

2http://www.nhc.noaa.gov/gccalc.shtml (for calculating the tropical storm wind radius)

http://www.ssd.noaa.gov/PS/TROP/floaters/07P/07P_floater.html

http://en.wikipedia.org/wiki/Tropical_cyclone#Size (for determining the average size of tropical cyclones.

http://earth.nullschool.net/#current/wind/isobaric/1000hPa/orthographic=-171.71,-20.83,1006

Edited by Vorticity0123
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Posted
  • Location: Eastbourne, East Sussex (work in Mid Sussex)
  • Location: Eastbourne, East Sussex (work in Mid Sussex)

Tonga: Warning - Tropical Cyclone Ian Category 4

 

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ROPICAL CYCLONE ADVISORY NUMBER TWENTY SEVEN (27) FOR TONGA ON TROPICAL CYCLONE IAN ISSUED FROM THE FUA'AMOTU TROPICAL CYCLONE WARNING CENTRE AT 7:30AM FRIDAY JANUARY 10TH 2014.

 
A TROPICAL CYCLONE WARNING
 
A HURRICANE WARNING REMAINS INFORCE FOR THE VAVAU GROUP.
 
A GALE WARNING REMAINS IN FORCE FOR HA'APAI AND NIUAFO'OU.
 
A STORM ALERT REMAINS IN FORCE FOR THE HA'APAI GROUP.
 
A TROPICAL CYCLONE ALERT REMAINS IN FORCE FOR TONGATAPU AND 'EUA.
 
A STRONG WIND WARNING REMAINS INFORCE FOR TONGATAPU,'EUA,NIUATOPUTAPU AND TAFAHI.
 
A HEAVY DAMAGING SWELL ADVISORY REMAINS INFORCE FOR COASTAL WATERS OF VAVA'U AND HA'APAI GROUP.
 
A HEAVY RAIN ADVISORY REMAINS IN FORCE FOR THE VAVA'U GROUP AND IS NOW INFORCE FOR NIUAFO'OU.
 
SEVERE TROPICAL CYCLONE IAN CATEGORY 4 WAS LOCATED NEAR 17 DECIMAL 0 SOUTH 175 DECIMAL 8 WEST OR ABOUT 160KM SOUTH OF NIUAFO'OU OR ABOUT 265KM NORTHWEST OF VAVA'U AT 6:00AM THIS MORNING.TROPICAL CYCLONE IAN HAS ESTIMATED WINDS OF 90KNOTS NEAR ITS CENTRE WITH MOMENTARY GUSTS UP TO 125KNOTS.THE CYCLONE CONTINUES TO INTENSIFY AND IS MOVING EAST AT 3KNOTS.
 
ON ITS CURRENT TRACK, TROPICAL CYCLONE IAN MAY BRING:
 
(1) DESTRUCTIVE STORM FORCE WINDS TO THE VAVA'U GROUP IN THE NEXT 12-18HRS AND WILL BE FOLLOWED BY A VERY DESTRUCTIVE HURRICANE FORCE WINDS IN THE NEXT 18-24 HOURS.
 
(2) DAMAGING GALE FORCE WINDS TO HA'APAI IN THE NEXT 18-24HRS.
 
(3) DESTRUCTIVE STORM FORCE WINDS TO THE HA'APAI GROUP IN THE NEXT 24 TO 48HRS
 
(4) DAMAGING GALE FORCE WINDS TO TONGATAPU AND 'EUA IN THE NEXT 24 TO 48HRS
 
WEATHER FORECAST FOR TONGA:
 
FOR THE VAVA'U GROUP:
 
WINDS INCREASING TO 45-55KTS WITH MOMENTARY GUST UP TO 65 T0 75KT IN THE NEXT 12-18HRS AND FURTHER INCREASING TO 65 KNOTS WITH GUST UP TO 85 IN THE NEXT 18-24 HOURS. OVERCAST WITH PERIOD OF RAIN DEVELOPING WITH SOME FLASH FLOODING EXPECTED.HIGH SEAS WITH DAMAGING HEAVY NORTHWEST SWELLS DEVELOPING.
 
FOR THE HA'APAI GROUPS:
 
WINDS INCREASING TO 30-35KT WITH MOMENTARY GUST TO 45-50KT IN THE NEXT 18 TO 24HR. CLOUDY PERIODS WITH OCCASIONAL SHOWERS DEVELOPING TO RAIN IN THE 18 TO 24HRS.SEAS BECOMING ROUGH TO VERY ROUGH WITH DAMAGING HEAVY NORTHWEST SWELLS DEVELOPING.
 
FOR NIUAFO'OU:
 
DAMAGING WINDS 30-35KTS WITH MOMENTARY GUSTS UP TO 50 KNOTS. RAIN HEAVY AT TIMES BUT DECREASING LATER TODAY.SEAS ROUGH TO VERY ROUGH WITH HEAVY NORTHWEST SWELL.
 
FOR NIUATOPUTAPU AND TAFAHI:
 
WINDS INCREASING TO 20-30KTS. CLOUDY PERIODS WITH OCCASIONAL SHOWERS. SEAS BECOMING ROUGH WITH MODERATE NORTHWEST SWELLS.
 
FOR TONGATAPU AND 'EUA:
 
EXPECT EAST TO SOUTHEAST WINDS 20-25KTS INCREASING TO 30-35 KNOTS IN THE NEXT 24-48 HOURS.
 
EXPECT RAIN, HEAVY AT TIMES IN THE NEXT 24-36 HOURS. ROUGH SEAS WITH HEAVY SWELLS DEVELOPING.
 
TEMPERATURE FORECAST FOR NUKU'ALOFA:
 
MIN: 25 DEGREES CELSIUS TONIGHT.
 
MAX: 31 DEGREES CELSIUS TODAY.
 
TIDE PREDICTIONS:
 
LOW TIDE : 08:55AM
 
HIGH TIDE : 03:15PM
 
THE MEAN SEA LEVEL PRESSURE RECORDED AT FUA'AMOTU AT 7:30AM WAS 1005.6MB
 
THE NEXT TROPICAL CYCLCONE ADVISORY ON TROPICAL CYCLONE IAN WILL BE ISSUED AROUND 10:00AM THIS MORNING

 

 

http://www.scoop.co.nz/stories/WO1401/S00097/tonga-warning-tropical-cyclone-ian-category-4.htm

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

Winds have risen to 120kts, cat 4 on the SS scale. The eye is nice and clear now and is surrounded by intense convection. An impressive little cyclone! Pretty rough on the islands of Tonga right now I would've thought!

 

post-1820-0-22372400-1389386441_thumb.jp

 

 

 

Edited by Somerset Squall
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Posted
  • Location: Eastbourne, East Sussex (work in Mid Sussex)
  • Location: Eastbourne, East Sussex (work in Mid Sussex)

Tropical Cyclone Ian Passing Tonga in South Pacific

 

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Tropical Cyclone Ian is moving to the south in the South Pacific Ocean, and it is located about 360 nautical miles southwest of Pago Pago. Ian will move well to the east of Australia and north of New Zealand through the next few days. Tropical Cylcone Ian is the first tropical cyclone of the South Pacific season, which typically runs from November through April. The current forecast path for Ian takes the center of the cyclone through the northern islands of Tonga and then just east of the island of Tongatapu where the capital city of Nuku'alofa is located. Ian is forecast to be the equivalent of a Category 4 hurricane as it makes its closest approach to Nuku'alofa early Saturday (U.S. time), according to the Joint Typhoon Warning Center.
 
Although the core of Ian is forecast to pass just east of Nuku'alofa, bands of heavy rain and gusty winds are still expected. After passing through Tonga, Ian will head to the southeast along the equatorial ridge; no other significant land areas are in the path of the cyclone. According to The Weather Channel's hurricane specialist Michael Lowry, ocean water temperatures in the mid-80s coupled with light wind shear is expected to allow Tropical Cyclone Ian to maintain intensity in the short term before gradually weakening. "Historically speaking, this is an uncommonly strong storm for the region," said Lowry.
 
"Going back to 1941, there have been 115 storms to pass within 50 miles of Tonga (1941-2012). That's 1-2 storms per year on average (within 50 miles of the archipelago). The intensity record is a bit fragmented, but of those 115 storms, only one or two near Ian's current (estimated) intensity can be found in that period of record."

 

 
 
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