Tropical Storm Erika Spaghetti Models, Satellite Image, Forecast Discussion

Tropical Storm Erika Satellite 1845Z IR Rainbow 09.02.09

Tropical Storm Erika NHC Forecast Track 2pm 09.02.09

for a more recent update on Erika, including spaghetti model, CLICK HERE

Tropical Storm Erika looks formidable on the satellite image but that can be deceiving.  Upper winds have been expected to start picking up from the southwest and disrupt the upper air circulation and outflow pattern.  It started earlier than anticipated.  The ridge in the Atlantic is expected to expand from its contracted phase following two big trofs the last two weeks.  For that reason, the storm has gone a bit farther west than earlier forecasts but certainly within the envelope presented by the various modeling data.  The majority of tracks on the spaghetti model take the storm northwest.  But there are some that advertise due west.  Shearing on models is showing an increase, which would suggest a potential distruction of the storm.  Yet, 5 models take it to category 2 level or greater.  This is counterintuitive.  The 12Z GFS wants to take a weak tropical low through the Florida Straits and then wrap it around back toward Tampa.  The NHC discussion below mentions potential dissipation but also does not have that it its forecast, given the models that differ with that solution.  Other models do in fact keep it very weak.   Conventional wisdom would suggest that this storm is in for trouble trying to develop, but the fact that some models want to go against that notion makes it worthy of continuation of monitoring.  There is no real consensus as to track or intensity.  My guess is that the official track will shifted again farther west, as this current track was shifted from the previous outlook.  But, evidence suggests that running it up to hurricane status should be difficult, unless the upper wind forecast data does not come to fruition.    National Hurricane Center 11AM Wednesday Forecast Discussion is below.

Tropical Storm Erika Spaghetti Model Track 12Z 09.02.09Trppical Storm Erika Spaghett Model Intensity 12Z 09.02.09

 

TROPICAL STORM ERIKA DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
1100 AM AST WED SEP 02 2009

VISIBLE SATELLITE IMAGES AND AIR FORCE RESERVE HURRICANE HUNTER
DATA SHOW THAT ERIKA IS A POORLY ORGANIZED SYSTEM.  THERE ARE
MULTIPLE SWIRLS APPARENT ON THE SATELLITE IMAGERY ROTATING IN THE
LARGER CIRCULATION ENVELOPE WITH A MEAN CENTER TO THE WEST OF THE
DEEP CONVECTION.  THE SFMR EARLIER REPORTED WINDS OF ABOUT 35
KT…WHICH IS IN GOOD AGREEMENT WITH SATELLITE INTENSITY
ESTIMATES…SO THAT VALUE WILL BE USED AS THE INITIAL INTENSITY. 

VERTICAL WIND SHEAR HAS INCREASED EARLIER THAN EXPECTED…WITH CIMSS
DIAGNOSING ABOUT 15-20 KT OF SHEAR. AT FIRST GLANCE…THE SHEAR DOES
NOT APPEAR TO BE TOO STRONG OVER THE SYSTEM WITH SOUTH OR
SOUTHEASTERLY WINDS REPORTED AT 200 MB OVER THE NORTHERN LEEWARD
ISLANDS. HOWEVER…UPPER-AIR DATA FROM GUADELOUPE AND ST. MAARTEN
SUGGEST THAT THE SHEAR IS PRIMARILY COMING FROM SOUTHWESTERLY WINDS
BETWEEN 300 MB-250 MB…AND THIS IS APPARENTLY UNDERCUTTING THE
OUTFLOW LAYERS AT 200 MB AND ABOVE.  MOST OF THE GLOBAL MODELS DO
NOT SHOW MUCH RELAXATION OF THIS SHEAR…AND ACTUALLY SHOW IT
INCREASING SIGNIFICANTLY IN A COUPLE OF DAYS.  DESPITE ALL THIS
SHEAR…ALL RELIABLE GUIDANCE RESTRENGTHENS THIS SYSTEM TO NEAR
HURRICANE STRENGTH IN A FEW DAYS.  THIS REINTENSIFICATION
DOES NOT SEEM VERY LIKELY AND THE NHC FORECAST IS MUCH LOWER THAN
THE GUIDANCE.  GIVEN THE POSSIBLE SHEAR DURING THE FORECAST
PERIOD…IT WOULD NOT BE SURPRISING IF ERIKA DISSIPATED.

A 24-HOUR MOTION IS ABOUT 275/9. A WEST-NORTHWESTWARD TRACK IS
PREDICTED TO RESUME AS THE STORM MOVES TO THE SOUTH OF A WEAK
SUBTROPICAL RIDGE FOR A COUPLE OF DAYS. THIS RIDGE IS FORECAST TO
WEAKEN SOMEWHAT IN A FEW DAYS…AND A NORTHWESTWARD MOTION IS
POSSIBLE BY THE END OF THE FORECAST. THE OFFICIAL FORECAST HAS BEEN
SHIFTED LEFT OF THE PREVIOUS ONE AND IS LEFT OF THE DYNAMICAL
CONSENSUS DUE TO THE ANTICIPATION OF ERIKA REMAINING WEAK. IT
SHOULD BE EMPHASIZED THAT…OVERALL…THIS IS A LOW-CONFIDENCE
TRACK FORECAST.

TROPICAL STORM WATCHES COULD BE REQUIRED FOR THE U.S. AND BRITISH
VIRGIN ISLANDS AS WELL AS PUERTO RICO LATER TODAY. 

FORECAST POSITIONS AND MAX WINDS

INITIAL      02/1500Z 16.5N  60.4W    35 KT
12HR VT     03/0000Z 16.9N  61.5W    35 KT
24HR VT     03/1200Z 17.4N  62.8W    40 KT
36HR VT     04/0000Z 18.0N  64.2W    45 KT
48HR VT     04/1200Z 18.6N  65.5W    40 KT
72HR VT     05/1200Z 20.0N  68.5W    35 KT
96HR VT     06/1200Z 21.5N  71.5W    30 KT
120HR VT     07/1200Z 23.5N  73.5W    30 KT

$$
FORECASTER BLAKE/FRANKLIN