eastern pacific Major Hurricane Iselle

[Somerset Squall]

The Eastern Pacific continues to produce storms with ernest with the formation of Tropical Storm Iselle this evening, located at 12.7N, 122.3E, about 1100 miles southwest of the southern tip of Baja California. Winds are at 35kts. Convection is wrapping nicely around the LLCC of Iselle, with good banding features in the southern and western quadrants. Shear is low on the west-northwest then westward track, and waters warm. Therefore, Iselle is forecast to become a hurricane. Just when this may occur is open to question. NHC mention a signifcant chance of rapid intensification over the next 24hrs, which would not be surprising given the rapidly improving structure and favourable environment. By day 5, Iselle will be nearing the Central Pacific basin, where it's likely to enter as a weakening storm.

Edited August 9, 2014 by Somerset Squall

[Somerset Squall]

Iselle strengthened quickly through today, and winds are at 55kts. In latest satellite imagery, Iselle has developed a large eye, so the storm should be upgraded to a hurricane very soon. Iselle has another day or two to strengthen before it reaches cooler waters and a more stable airmass.

 

 

 

[Somerset Squall]

Iselle is now a 65kt hurricane. The eye I mentioned last night is currently cloud obscured, but the central dense overcast remains solid. A llitte more intensification is expected before Iselle runs into drier, more stable air, and cooler sea temps.

[Somerset Squall]

Iselle has strengthened more than forecast, and winds are now at 85kts, cat 2 on the SS scale. A clear eye emerged from the central dense overcast earlier, but has since become cloud filled. Iselle will be reaching cooler waters in about 12-24hrs time, so any further strengthening will need to happen within this time.

[Somerset Squall]

Iselle has strengthened a little more, to 95kts. Time is running out for further intensification however, as drier, more stable air lurks to the west. Iselle does have a small shot at becoming a major hurricane however (100kts).

[Somerset Squall]

Iselle has become a major hurricane, the season's third, with winds of 100kts. Iselle is probably peaking a it looks like it is running into a more stable environment. However, for now, shear is low, so weakening will be slow. Iselle is heading westwards, but is expected to gain some lattitude and approach Hawaii in the extended range, though the system will be considerably weaker at this stage.

 

 

[Somerset Squall]

Iselle has strengthened yet further, with winds now at 110kts. Iselle has also become an annular hurricane, characterised by a complete loss of banding features, a large eye, and a circular ring of convection compassing the eye. Annular hurricanes tend to create their own environment and sheild themselves from dry air. Thus, only very slow weakening can be expected over the next couple of days, before shear increases.

[Somerset Squall]

Iselle continues to defy forecasts and has become a category 4 hurricane, with winds of 120kts. The structure remains "doughnutlike" with a large, well defined eye, encircled with deep convection, but no banding.

[Somerset Squall]

Impressive Iselle:

 

 

 

[summer blizzard]

Very pretty. How strong was the hit on Hawaii last year. She could well still be a hurricane at impact. 

 

Unfortunately for the category 4 whopper they got years back, you need it to approach from the S/SE/SW recurving.

[Somerset Squall]

Very pretty. How strong was the hit on Hawaii last year. She could well still be a hurricane at impact. 

 

Unfortunately for the category 4 whopper they got years back, you need it to approach from the S/SE/SW recurving.

 

Flossie was at 35kts, on the verge of weakening to 30kts when it impacted Hawaii I think. Iselle could well be stronger, especially as it is so much stronger than Flossie was to start with anyway.

[tropicbreeze]

Usually systems moving in from the east or south east run into cold water and weaken rapidly. Iselle seems to be immune to this. Does becoming annular virtually give it a "coat of armour"?

[Somerset Squall]

I don't know a huge deal about annular hurricanes, but they tend to weaken more slowly than typical hurricanes in poorer environments. Kold Weather's hurricane tutorial pinned at the top of the hurricane forum sheds some light on it. Annular hurricanes tend to create there own cocooned environments, your anaology of a "coat of armour" is a good one.

[Somerset Squall]

Iselle is moving through some very dry air, but this hasn't punctured the doughnutlike ring of convection surrounding the large eye just yet. Winds are down just slightly, to 110kts, a high end cat 3 on the SS scale. Even annular hurricanes can't stave off an unfavourable environment forever, and higher shear resides to the west, which should eventually drive the dry air through the ring of convection. NHC expect Iselle to lose it's annular structure tonight, then faster weakening should occur. Iselle is still expected to be a tropical storm when it impacts Hawaii however. Even a tropical storm can be dangerous for Hawaii, which is highly mountainous, which means rains from Iselle is likely to bring flooding and mudslides.

Edited August 5, 2014 by Somerset Squall

[tropicbreeze]

Thanks SS, I checked that tutorial. Will have to do a lot more reading in there as time permits. Every time I feel I've notched up a bit more knowledge on the subject it also reveals there's a lot more I don't know. Almost a "one step forward two steps back" situation.

[summer blizzard]

Now at 100mph.

[Vorticity0123]

After having almost all convection dissipated, Iselle is rapidly becoming more organized, as a circular, though ragged, eyewall has developed. And this has all occurred in a harshly dry environment. (as indicated by the yellow colours in the water vapor imagery loop below) What a unique system!

 

Water vapor satellite loop of Iselle (Courtesy: NOAA)

 

Source:

http://www.ssd.noaa.gov/PS/TROP/floaters/09E/imagery/wv_lalo-animated.gif

[Gael_Force]

The big island doesn't look so big with that approaching.

 

[knocker]

Hawaii is under a Hurricane Warning for the 1st time in 22 yrs. Wind animation map shows the destructive Storm/storms http://earth.nullschool.net/#current/wind/surface/level/orthographic=-142.98,18.54,3000 â€¦

[Somerset Squall]

Iselle's annular history is definitely playing a part here. The only thing that can destroy it is shear. And as that is low, Iselle refuses to weaken. Intensity fell to 75kts, but is back up to 80kts. I would not be surprised if Iselle manages to get a bit stronger given current trends. A landfalling hurricane on Hawaii- that's a rare feat.

Edited August 6, 2014 by Somerset Squall

[Somerset Squall]

Iselle made landfall as a high end tropical storm as higher shear disrupted Iselle's core. Land interaction with the mountains of the Big Island of Hawaii have truly done a number on Iselle, and there is not much left of Iselle on the other side. There is barely any convection associated with the system anymore and the circulation is broad and diffuse, and consists of many ill defined swirls. Although shear is lower and waters warmer northwest of Hawaii, Iselle appears too weak to re-intensify. Winds are at 45kts associated with the low, but a well defined circulation no longer exists.

[summer blizzard]

What a shred!