TROPICAL DISTURBANCE INVEST 99L SYNOPSIS OCT. 19, 2010 ISSUED 10:50 A.M. EDT

Good day everyone!

UPDATE: SPECIAL TROPICAL WEATHER OUTLOOK

000
ABNT20 KNHC 192039
TWOAT 
SPECIAL TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
440 PM EDT TUE OCT 19 2010

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

OBSERVATIONS FROM AN AIR FORCE RESERVE UNIT RECONNAISSANCE AIRCRAFT
INVESTIGATING THE AREA OF LOW PRESSURE...ABOUT MIDWAY BETWEEN
HONDURAS AND THE CAYMAN ISLANDS...INDICATE THAT A BROAD LOW-LEVEL
CIRCULATION HAS FORMED.  CONDITIONS APPEAR CONDUCIVE FOR SOME
DEVELOPMENT...AND ANY INCREASE IN THE ORGANIZATION OF THE
ASSOCIATED SHOWERS AND THUNDERSTORMS COULD LEAD TO THE FORMATION OF
A TROPICAL DEPRESSION.  INTERESTS IN THE NORTHWEST CARIBBEAN SEA
SHOULD MONITOR THE PROGRESS OF THIS SYSTEM.  THERE IS A HIGH
CHANCE...70 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS AS IT MOVES TOWARD THE NORTH AT 5 TO 10
MPH. 

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

 

INVEST 99L:
Tropical Disturbance INVEST 99L has become a little better organized overnight, and recent satellite loop imagery indicates that further slow organization may be occurring.  Although the latest ASCAT pass indicates there is not yet a closed LLC  as of yet, close up views of Visbile and RGB satellite loop imagery indicate a center located near 17.3N;83.2W.

99L RGB LOOP
http://www.ssd.noaa.gov/goes/flt/t1/flash-rgb-s.html

Based on the current wind shear product from CIMSS, the disturbance center is just north of the center of an established upper level anticyclone.  Although not optimal, the disturbance is being aided by the northern outflow jet, and outflow on the northern side of the system is excellent, while outflow to the south is restricted.  The flow associated with this upper level anticyclone over the area and near the center, is running only 15 kts or less.  Upper level divergence is excellent, however lower level convergence is somewhat limited, but may improve with the upper level feature being in place.
CURRENT WIND SHEAR MAP

UPPER DIVERGENCE

LOWER CONVERGENCE

The current wind shear forecast indicates the upper level winds to be mainly favorable for the next 12-24 hours, before shear increases on the western side of the disturbance .  However, depending on forward speed and track, this may not hinder development too much, but may limit intensity.  Based on these factors, I believe we should see more slow organization and development throughout the day, and it is possible we may see another Tropical Depression within the next 24-48 hours.

SHEAR FORECAST

As far as motion, I am not even going to look at model guidance as of yet, until at least the system becomes pretty much established.  As I analyzed the computer models this morning, the conditions of a “Paula” type scenario came to mind, as far as accuracy in computer models forecast track.  If you remember, the model guidance was quick in the beginning couple of days to quickly “push” Paula southward and SW, in which we saw later, was not the case.  This system will be in the best interest of all, to again be forecast on a daily basis regarding steering currents as the current steering is weak, and not much unlike the pattern we saw with Paula during her first few days.  One thing I do notice however, is that the models, based on satellite loop imagery, have initialized this too far south and west.  Based on this, and analysis of current and forecast steering layers maps, I feel we will see a lsow motion toward the north, or NNW early today, and possibly toward the NNE for a brief period thereafter.  Again, steering currents are weak, and may remain that way for the next 48 hours…in fact, satellite loop imagery indicates this may even be almost stationary at the moment.

CURRENT STEERING

Given the complex nature of the steering regime, I cannot rule out at the moment, that this meanders around in the NW Caribbean, and eventually heads for the Yucatan channel in a few days as ridging builds in north of the area.  Again, this is just ONE possible scenario.  The other possibility is that an approaching trof, prior to the ridge building back, may take this on a path similar to Paula, except off to the NE.  Given the models have this a little more south and west, I cannot buy the push W or SSW later into central America at the moment.

I will continue to monitor 99L for any significant changes, and will monitor steering currents on and off throughout the day.

Elsewhere, an area of low pressure still persists in the eastern Atlantic, however it is void of convection, and development is not expected.

Elsewhere, Tropical Storm formation is not expected through Wednesday.

T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST/TROPICAL FORECASTER
MEMBER WEST CENTRAL FL AMS (webmaster)
CERTIFIED SKYWARN OFFICIAL STORM SPOTTER (advanced)