Tropical Storm Iselle

[James M]

We know have Tropical Depression Ten-E in the East Pacific:

NIGHTTIME VISIBLE AND INFRARED SATELLITE IMAGERY...PLUS A 13/1017Z

TRMM MICROWAVE OVERPASS...INDICATE THE TROPICAL DISTURBANCE

LOCATED ABOUT 185 NMI SOUTH-SOUTHWEST OF MANZANILLO MEXICO HAS

BECOME MUCH BETTER ORGANIZED AND HAS DEVELOPED INTO TROPICAL

DEPRESSION TEN-E. CURVED BANDING NOTED IN THE TRMM OVERPASS

SUGGESTS THIS SYSTEM MAY ALREADY BE NEAR TROPICAL STORM

STRENGTH...BUT THE RAPID CONVECTIVE ORGANIZATION MAY NOT HAVE

TRANSLATED INTO AN INCREASE IN THE SURFACE WINDS.

THE INITIAL MOTION ESTIMATE IS 280/09 KT. TROPICAL DEPRESSION 10-E

IS EXPECTED TO MOVE IN A GENERAL WEST OR WEST-NORTHWESTWARD

DIRECTION AS THE CYCLONE IS STEERED BY A DEEP-LAYERED RIDGE

SITUATED TO THE NORTH OF THE SYSTEM. THE LAST GFDL MODEL RUN

APPEARS TO BE AN OUTLIER BACK TAKING THE DEPRESSION NORTHWARD

TOWARD SOUTHERN BAJA CALIFORNIA. THE REST OF THE NHC MODEL SUITE

TAKES THE SYSTEM SLOWLY WEST-NORTHWESTWARD. THE OFFICIAL FORECAST

TRACK IS ALONG THE EXTREME SOUTHERN PORTION OF THE GUIDANCE

ENVELOPE IN ANTICIPATION OF INCREASING VERTICAL WIND SHEAR POSSIBLY

WEAKENING THE CYCLONE IN THE LATER PERIODS...WHICH WOULD CAUSE THE

SYSTEM TO BE STEERED MORE WESTWARD BY THE LOW-LEVEL EASTERLIES.

ALTHOUGH THE OVERNIGHT BURST OF CONVECTION WAS IMPRESSIVE AND

HELPED TO QUICKLY SPIN UP THE WIND FIELD...THIS DEVELOPMENT PROCESS

MAY BE SHORT-LIVED. THE CONVECTIVE BURST MAY HAVE BEEN IN RESPONSE

TO THE DIVERGENT REGION OF AN APPROACHING UPPER-LEVEL JET MAXIMUM

MOVING ACROSS SOUTH-CENTRAL MEXICO. HOWEVER...WATER VAPOR IMAGERY

AND DERIVED WIND FIELDS ALSO INDICATE THAT THE NOSE OF THE 40-50 KT

UPPER-LEVEL JET SHOULD BE ENCROACHING ON THE CYCLONE FROM THE

NORTHEAST DURING THE NEXT 24 HOURS...WHICH SHOULD SIGNIFICANTLY

INCREASE THE VERTICAL WIND SHEAR ACROSS THE SYSTEM. FOR THIS

REASON...ONLY MODEST INTENSIFICATION IS FORECAST THROUGH DAY 2 WITH

GRADUAL WEAKENING EXPECTED AFTERWARD AS THE CYCLONE MOVES OVER

COOLER WATER.

FORECASTER STEWART/BROWN

Edited August 13, 2008 by James M

[Cookie]

expected to make tropical storm by tonight

[Somerset Squall]

TD10E has intensified over the last 6 hours, and has become Tropical Storm Iselle, with an intensity of 35kts. Conditions are not favourable for any further significant intensification, as shear is increasing and is set to remain high over the next few days. Beyond 96hrs, waters will also cool which will induce weakening. Iselle is not expected to affect land.

[Cookie]

their staying away from land well at the moment

[Somerset Squall]

their staying away from land well at the moment

Yes, thankfully. The East Pacific is generally the least deadly basin because most storms track west-northwestwards away from land. For this reason most years have no names retired because it's not all that common for storms to track northwards or northeastwards to make landfall in Mexico, as pressure is generally higher here which acts as a barrier against tropical cyclones. Of course, there are exceptions, Pauline in 1997 was very deadly for example.

[Somerset Squall]

Iselle has intensified a little overnight, and is now at 40kts. Convection remains deep to the southwest of the LLC, and this shows that Iselle is in a highly sheared environment. Because of this, the NHC show little or no further strengthening in their latest forcast. Iselle will continue to head west-northwestward or northwestward over the next few days and weakening will commence in a couple days time as Iselle moves over cooler waters and shear remains high. If shear gets any stronger it's possible Iselle may dissipate before it reaches the cooler waters.

[Somerset Squall]

Iselle reached 45kts this afternoon, but has since weakened back to 40kt. Iselle remains very lop sided with the deep convection lumped to the southwest of the partially exposed LLC, a classic example of a storm struggling against shear. Shear has been analysed to be around 20-30kts which is pretty high, therefore the most likely option for Iselle is weakening from here on in, as the shear is not expected to ease. Cooler waters await Iselle in around 48hrs, which should kill off the system if this shear doesn't. A very hostile environement indeed, the conditions rapidly went downhill after Iselle formed which means the system should remain a weak tropical storm at best over the next 24hrs.

[Somerset Squall]

Iselle is battling on, but it seems like she is losing the fight against that strong shear. Iselle is just about a tropical storm this morning with the intensity reduced to 35kts. Convection has reduced in coverage and remains to the southwest of the circulation centre. Iselle could degenerate into a remant low by 36hrs, sooner if the convection continues to vanish like it's doing currently. It appers the sea temps will not play a great role in the dissipation of Iselle, as Iselle may well succumb to the shear whilst still over warm waters. If it survives longer than forecast, then the cold waters to the northwest will definitely finish the job.

[Somerset Squall]

Iselle has finally given up. Convection has compltely dissipated and Iselle has been declared a remnant low. Regeneration is not expected due to continued high shear and cool sea temps.

[Cookie]

thanks for all the updates mate

[Somerset Squall]

Convection has increased slightly with the remnant low of Iselle, and the NHC have therefore placed a low risk of redevelopment on the system. It's unlikely, but a possibility.

[Somerset Squall]

Believe it or not, the remnant low of Iselle is still in tact, and today, there has been some limited convection developing near the centre. Iselle's remnants have been steered southwestwards since dissipation as a tropical storm and they now are over warmer waters around 13N, 127W. The circulation has remained closed but it would take some good conditions for Iselle to recover, if at all. Shear is moderate near the remnants but this is certainly a lot lower than the horrendous shear it had to battle back when it was a tropical cyclone. Maybe something to keep an eye on, I wouldn't like to say what chances, if any, it has of re-development.

Infrared of the East Pacific, showing the remnant low of Iselle:

Satellite image of the well defined low, however, convection would need to increase a lot more if re-development was to occur:

[Cookie]

they never give up do they :lol:

[Somerset Squall]

Convection has continued to increase with the remnant low of Iselle, however, the convection is displaced from the LLC so re-development is unlikely. However, due to the increase in convection, the NHC have put it at a low risk of tropical depression formation in the next 48 hours.

[Cookie]

will it still be the same name yeah?

[Somerset Squall]

will it still be the same name yeah?

If (it's unlikely) the remnant low manages to re-organise into a tropical depression then yes, it would be called Iselle. Convection remains disorganised and has decreased a little since earlier today. Since it ceased to be a tropical cyclone 5-6days ago it would be very interesting if did manage to pull the re-development off!

[Cookie]

ok thanks.