south indian ocean Very Intense Tropical Cyclone Hellen

[Somerset Squall]

A tropical depression has formed in the northern Mozambique Channel, off the coast of Mozambique. 14 is in an area of low shear, warm sea temps and good outflow. Banding features are readily taking shape and convection is steadily increasing over the LLCC. As 14 moves southeast away from the coast, it should intensify. Track forecast is uncertain, but a southeastward track followed by bend to the southwest is forecast by MeteoFrance, as steering transfers from a ridge to the north to a developing ridge to the south. Shear could rise further south in the Mozambique Channel, which could initiate weakening in a few days time.

Edited March 30, 2014 by Somerset Squall

[Vorticity0123]

TD 14 looks rather well-organized, looking at the latest satellite imagery (20Z, 28-03-2014). Curved, though fragmented, bands, have developed to the north and south of the system. Central convection has also taken a somewhat fragmented appearance. Below is a visible image of TD 14:

 

 

Currently, models are quite spread out concerning the track forecast of TD 14. While the GFS and UKMET are forecasting a continued southeastward track toward Madagascar (and no southwestward track in the end), the CMC-model forecasts a track hugging the African coast. This in turn results in a high level of uncertainty in the near- and far-future of TD 14, as Somerset Squall mentioned.

 

EDIT; JTWC has updated the low to TD 21, with an initial intensity of 35 kt. The JTWC forecasts a similar track as RSMC la Reunion, initially moving southeast before bending back to the west in the later timeframes. Intensity wise, the tropical cyclone is forecast to intensify up to 50 kt in about 72 hr, before weakening back toward a tropical depression at the end of the forecast period.

Of a side note, the designation TD 14 has been given by RSMC la Reunion, while the designation TD 21 has been assigned by the JTWC.

 

Sources:

http://moe.met.fsu.edu/cyclonephase/cmc/fcst/archive/14032812/index.html

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

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

Edited March 28, 2014 by Vorticity0123

[Somerset Squall]

MeteoFrance has upgraded the system to Moderate Tropical Storm Hellen. JTWC have raised the winds to 45kts in their latest advisory. Hellen has well established banding wrapping tightly into the well defined LLC. Hellen is benefitting from an environment of low shear and robust poleward outflow, which should allow further intensification of Hellen as it drifts towards the southeast. Steering currents are very weak, but a slow drift to the west is expected before Hellen can reach the northwest coast of Madagascar. As Hellen moves west, shear is expected to increase, bringing about weakening then dissipation over water.

[Vorticity0123]

Hellen continues to steadily become more organized, with deep convection now completely encompassing the LLCC (low level circulation centre). In fact, the pattern quite much resembles a CDO (central dense overcast). Furthermore, a well-defined band of convection is wrapping around the eastern and southern quarters of the cyclone. 

 

Due to this increase in organization, CIMSS ADT satellite intensity estimates have been on the rise, currently yielding an intensity of 59 kt (knots). This is quite a few kt higher than the JTWC intensity estimate (14 kt difference). The ADT satellite intensity estimate seems reasonable, given the very intense (though slightly elongated east-west) CDO, with no eye feature yet apparent.

 

The ADT intensity estimate trend of Hellen can be seen below:

CIMSS ADT satellite intensity estimate trend.

 

Given the well-organized appearance of Hellen, continued strengthening seems likely, until shear increases, as Somerset Squall mentioned. The JTWC forecasts Hellen to peak at 65 kt in about a day or so. Given the current satellite appearance, it seems like the forecast may be somewhat conservative.

 

The track forecast remains of much lower confidence. While the GFS forecasted Hellen would move southward along the coast of Madagascar in the extended timeframe, this time the latest UKMET-run forecasted a comparable track as the previous GFS-run. The latest GFS-run, on the contrary, has become more in line with the official forecasts from JTWC and La Réunion. Due to the weak steering currents, the official track forecasts may flip-flop somewhat in the near future.

 

Sources:

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

http://en.wikipedia.org/wiki/Central_dense_overcast

http://www.ssd.noaa.gov/PS/TROP/floaters/21S/21S_floater.html

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

http://moe.met.fsu.edu/cyclonephase/ukm/fcst/archive/14032912/index.html

Edited March 29, 2014 by Vorticity0123

[Somerset Squall]

JTWC have upped the winds to 60kts in their latest advisory, and now forecast a peak of 95kts, with this intensity beig reached fairly rapidly due to low shear, and continued excellent outflow.

[Somerset Squall]

Hellen is bombing. Winds are now up to 90kts (1 min sustained), and an eye has popped out of the central dense overcast and is clearing out nicely.

 

 

[Sainsbo]

It's amazing to see how fast things can change. JTWC going for a peak intentisy of 120kts (138mph) which would make it a solid category 4.

[Somerset Squall]

What a beauty! Hellen's eye has become even more defined this morning, and NRL site puts the intensity at 115kts, making Hellen a cat 4 on the SS scale. This suggests that Hellen could peak higher than 120kts of current trends continue.

 

 

This cyclone has caught both JTWC and MeteoFrance off guard, but particularly MeteoFrance. Initial forecasts from MeteoFrance suggested Hellen wouldn't make it past the "Moderate Tropical Storm" classification, which is for storms with winds between 34 and 47kts!

 

 

 

 

[Somerset Squall]

Hellen has intensified by 80kts in 24hrs, which can only be described as a bombing cyclone. Winds are now at 130kts, a high end cat 4 on the SS scale. JTWC forecast Hellen to become the second cat 5 of 2014 in the next 12hrs (if this does occur, it will be the third cat 5 in the South Indian Ocean this 2013-14 season, which is an extremely rare occurrence to my knowledge. The others were Bruce and Gillian).

[Vorticity0123]

It's amazing to see how fast things can change. JTWC going for a peak intentisy of 120kts (138mph) which would make it a solid category 4.

 

This cyclone has caught both JTWC and MeteoFrance off guard, but particularly MeteoFrance. Initial forecasts from MeteoFrance suggested Hellen wouldn't make it past the "Moderate Tropical Storm" classification, which is for storms with winds between 34 and 47kts!

 

It was clear that, yesterday, Hellen was intensifying more quickly than the JTWC and RSMC la Réunion forecasted, but that it would lead to this... Incredible! JTWC has ramped up the maximum wind speed to 130 knots, making Hellen a very dangerous category 4 tropical cyclone on the SSHS-scale. In fact, they expect Hellen would peak as a category 5 tropical cyclone, with 140 kt winds at peak intensity!

 

The burst of rapid intensification has been highly impressive, with an increase in winds of 95 kt in just 42 hours, equivalent to almost 2.25 kt per hour! A comparable RI (rapid intensification) event occured with tropical cyclone Gillian, just a week ago:

 

http://en.wikipedia.org/wiki/Cyclone_Gillian_(2014)

 

Unfortunately, it appears to be becoming more and more likely that the northwestern tip of Madagascar could be severely impacted by Hellen. To show the possible impacted areas, below is the track forecast from the JTWC:

 

Even despite the center of Hellen is expected to remain away from land, the large size combined with the high intensity of the tropical cyclone means that the area could still be impacted by winds up to hurricane force. The area is mostly sparsely populated, except a small area which is located in the estuary of a river. A map of the population densities of Madagascar can be seen below:

 

 

EDIT: The JTWC has changed their track forecast and now anticipate landfall on Madagascar itself. This is rather worrying news.

 

Sources:

http://www.nrlmry.navy.mil/tc-bin/tc_home2.cgi?PHOT=yes&AGE=Latest&ACTIVES=14-SHEM-21S.HELLEN,14-WPAC-95W.INVEST&ATCF_BASIN=sh&SIZE=thumb&NAV=tc&ATCF_YR=2014&ATCF_FILE=/SATPRODUCTS/kauai_data/www/atcf_web/public_html/docs/warnings/2014/sh212014.14033000.wrn&CURRENT_ATCF_FILE=/SATPRODUCTS/kauai_data/www/atcf_web/public_html/docs/warnings/2014/sh212014.14033000.wrn&CURRENT=20140330.0610.metop-a.ASCAT_AMB_VIS.wind.21SHELLEN.5122_050pc_115kts-937mb_144S_443E_sft20140330_0600.jpg&CURRENT_ATCF=sh212014.14032918.wrn&ATCF_NAME=sh212014&ATCF_DIR=/SATPRODUCTS/kauai_data/www/atcf_web/public_html/docs/warnings/2014&MO=MAR&BASIN=SHEM&STYLE=tables&YEAR=2014&YR=14&STORM_NAME=21S.HELLEN&ARCHIVE=active&AREA=pacific/southern_hemisphere&DIR=/SATPRODUCTS/TC/tc14/SHEM/21S.HELLEN/ssmi/scat/scat_ambiguity&TYPE=ssmi&PROD=warn&SUB_PROD=scat_ambiguity

http://en.wikipedia.org/wiki/2013%E2%80%9314_South-West_Indian_Ocean_cyclone_season#Intense_Tropical_Cyclone_Hellen

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

http://www.usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/warnings/sh2114web.txt

http://www.marysrosaries.com/collaboration/images/thumb/e/e5/Madagascar_Population_Density_and_Ethnic_Groups_Map_1976.jpg/335px-Madagascar_Population_Density_and_Ethnic_Groups_Map_1976.jpg

Edited March 30, 2014 by Vorticity0123

[Somerset Squall]

Latest imagery shows Hellen's eye very close to the coast, it'll take a sharp turn west to avoid a landfall at this rate.

[Somerset Squall]

Hellen has been upgraded to a "Very Intense Tropical Cyclone" by MeteoFrance, with pressure estimated to be at 925mb.

[Somerset Squall]

Hellen peaked at 135kts, just shy of cat 5. Hellen has now weakened to 125kts due to land interaction and dry air entrainment. The dangerous cyclone has stubbornly continued southeast, so landfall is now imminent on northwestern Madagascar. Hellen will spend a while over land, before possibly emerging over the Mozambique Channel when the westward turn finally materialises. It is then expected to move across the channel before making a second landfall, this time on the coast of Mozambique. Significant reintensification over the channel appears unlikely due to the presense of moderate shear and dry air at the lattitude Hellen emerges over water.

[Vorticity0123]

Hellen is currently located just to the north of Majunga, in the northwestern part of Madagascar (as of MeteoFrance). Although the cyclone has weakened rapidly over the past few hours (the minimum central pressure has come up to 975 kt according to MeteoFrance), the threat of heavy rain, gusty winds and high storm surge remains over the island. Below is a satellite image of the rapidly weakening cyclone:

 

Satellite image of Hellen (Courtesy: NOAA)

 

The eye has clearly disappeared, and the convective envelope has also shrunk in size considerably. Unfortunately, Most of the shower activity associated with Hellen is located over land.

 

Wunderblogger Jeff Masters also has an interesting article about the very dangerous tropical cyclone, emphasizing the threat of storm surge the tropical cyclone may have.

 

http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2655

 

EDIT: The observed weakening has been stated as "unexpected" by NOAA. They state that:

 

 

 

FOR THE LAST 6 HOURS, HELLEN HAS VERY RAPIDLY WEAKENED. DT DVORAK HAS BEEN READJUSTED AT 5.0 AT 00
00Z (PREVIOUSLY ANALYSED AT 5.5). DESPITE THIS, THE DVORAK CONSTRAINTS HAVE BEEN BROKEN WITH A WEA
KENING OF 1.5 ON 6 HOURS. THERE ARE NOT CLEAR EXPLANATIONS FOR THIS WEAKENING EXCEPT THE STRENGHTE
NING OF A NORTH-EASTERLY TO NORTHERLY CONSTRAINT WITHIN THE UPPER LEVEL LAYERS. THE LOW LEVEL CENT
RE HAS BEEN LOCALIZED THANKS TO 0242Z MW WINDSAT PICTURE.

 

This might be an absolute relief for the citizens living in the northwestern part of Madagascar, as a major tropical cyclone landfall appears to be becoming unlikely. If impacts of Hellen have not already been very severe, it may mean that the impact is going to be much lighter than expected.

 

Finally, an article from Jo Farrow (Netweather) about TC Hellen can be found below:

 

http://www.netweather.tv/index.cgi?action=news;storyid=5782;sess=

 

Sources:

http://www.meteo.fr/temps/domtom/La_Reunion/meteoreunion2/

https://maps.google.nl/maps?hl=nl&tab=wl

http://weather.noaa.gov/pub/data/raw/wt/wtio30.fmee..txt

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

http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2655

Edited March 31, 2014 by Vorticity0123

[knocker]

http://rammb.cira.colostate.edu/products/tc_realtime/loop.asp?product=4kmirimg&storm_identifier=SH212014&starting_image=2014SH21_4KMIRIMG_201403310230.GIF

[Vorticity0123]

It is amazing to see how quickly tropical cyclones can fall apart! JTWC has issued their last advisory on Hellen, which has moved further inland. There is still a chance of regeneration, though, as stated by the JTWC:

 

 

 

NUMERIC MODEL GUIDANCE IS
TRACKING TC 21S BACK OVER THE MOZAMBIQUE CHANNEL WITH A CHANCE OF
REGENERATION WHILE MOVING TOWARDS THE AFRICAN LANDMASS.

 

Fortunately, due to this rapid weakening, Madagascar appears to have escaped the worst-case scenario. Furthermore, the strongest winds of the cyclone affected a very sparsely populated area. Mahajanga, a large city located to the northeast of the landfall location of Hellen, experienced a total amount of 156 mm of precipitation, but the winds were relatively light, given that the maximum wind gust reported in the city was only 76 km/h¹.

 

Sources:

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

¹: http://www.weather.com/news/weather-hurricanes/tropical-cyclone-hellen-rapid-intensification-madagascar-20140330

Edited April 1, 2014 by Vorticity0123