TROPICAL STORM DON / TROPICAL DISTURBANCE INVEST 96L FORECAST SYNOPSIS…ISSUED JUL. 18, 2017…12:20 P.M. EDT

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(T. F. “Storm” Walsh III)

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STORM W’s SEASONAL HURRICANE FORECAST
TOTAL STORMS: 14-16
HURRICANES:       6-8
MAJ. HURRICANES: 3-4

CURRENT TOTALS
STORMS: 4
HURRICANES: 0
MAJ. HURRICANES: 0

U.S. LANDFALLS: 1

Good day all!

Tropical Storm DON continues to head toward the Windward Islands this morning, and has weakened slightly.  The following information was available on DON, as of the 11:00 a.m. EDT advisory from the NHC :

11:00 AM AST Tue Jul 18
Location: 11.5°N 58.0°W
Moving: W at 20 mph
Min pressure: 1011 mb /  29.85 in
Max sustained: 40 mph

HURREVAC NHC TRACKING MAPS

DON SATELLITE LOOP (CLICK)

DON CURRENT WIND SHEAR FROM CIMSS

CARIBBEAN RADAR CANVAS (CLICK FOR ANIMATIONS)

Tropical Storm DON has weakened since the 8:00 a.m. intermediate advisory, with maximum sustained winds down to 40 mph.  Based on the most recent wind shear map from CIMSS, DON is beginning to lose the upper level support he had yesterday, and is beginning to encounter some slight westerly wind shear.

Based on my analysis of the wind shear forecast from the GFS model, the trend of increasing westerly shear should continue.  It is also noted in current water vapor loop imagery, that some dry air appears to be encroaching on the system, and the storm may begin to entrain some drier air later today or this evening.  Based on this new development, which was a change from information analyzed in yesterdays forecast, I have to concur with the new intensity scheme from the NHC.  Based on these criteria, DON may dissipate within the next 36 hours, if not somewhat sooner, depending on how quickly and how strong westerly shear develops.

NHC INTENSITY FORECAST

INIT 18/1500Z 11.5N 58.0W 35 KT 40 MPH
12H 19/0000Z 11.7N 60.9W 35 KT 40 MPH
24H 19/1200Z 12.0N 65.0W 30 KT 35 MPH
36H 20/0000Z…DISSIPATED

GOES EAST WATER VAPOR LOOP (RAMSDIS)

DON continues to move toward the west, at a pretty good forward speed.  Based on my analysis of current and forecast steering layers maps, I see really no change is track, or forecast track, as DON should remain in a strong east to west flow of the southern periphery of the sub-tropical ridge.  I concur with the NHC forecast track, and consensus of the dynamic model guidance.

DYNAMIC GUIDANCE

The following is information regarding the current watch/warning areas, and effects that will be associated with the storm.

DON WATCH/WARNING GRAPHIC

WATCHES AND WARNINGS
——————–
CHANGES WITH THIS ADVISORY:

The government of St. Lucia has discontinued the Tropical Storm
Watch for St. Lucia.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for…
* Grenada
* St. Vincent and the Grenadines

A Tropical Storm Watch is in effect for…
* Barbados
* Bonaire

Interests in Trinidad and Tobago, Aruba, and Curacao should monitor
the progress of Don.

For storm information specific to your area, please monitor
products issued by your national meteorological service.

Reports from an Air Force Reserve reconnaissance aircraft indicate
that the maximum sustained winds have decreased to near 40 mph (65
km/h) with higher gusts. Little change in strength is forecast
before Don moves through the Windward Islands. The tropical storm
is forecast to degenerate into a trough of low pressure late
Wednesday or Wednesday night.

Tropical-storm-force winds extend outward up to 35 miles (55 km)
from the center.

The estimated minimum central pressure is 1011 mb (29.86 inches).

HAZARDS AFFECTING LAND
———————-
WIND: Tropical storm conditions are expected in the warning area
by late this afternoon and tonight. Tropical storm conditions are
possible in the watch area by tonight.

RAINFALL: Don is expected to produce total rain accumulations of
3 to 6 inches, with isolated higher amounts across Barbados,
Trinidad and Tobago, and the southern Windward Islands through
Wednesday. These rains could produce life-threatening flash floods
and mudslides, especially in mountainous areas.

The following are projected rainfall accumulation totals out to 48 hours from the GFS and ECMWF models.

GFS

ECMWF

I should have another update on DON sometime tomorrow.

Elsewhere, the area of disturbed weather located to the east of DON, has been designated INVEST 96L.  Analysis of satellite loop imagery this morning indicated that 96L is currently disorganized.

INVEST 96L SATELLITE LOOP (CLICK FOR LOOP)

Based on the current and forecast wind shear products, 96L should move under the current upper level anticyclone to its NW.  This upper feature is currently forecast to remain near or over the disturbance during the next 42 hours, before dissipating, with westerly shear taking over after that time.  Based on this, the disturbance may have a chance at becoming a depression during the next 36 hours.  One negating factor may be, albeit INVEST 96L has a high value TPW signature, the disturbance will be moving into a large area of dry air during the same time period.  IF it can fight of the dry air given the TPW (Total Precipitable Water), there could be a very slim probability of it attaining brief Tropical Storm status, however looking at the amount of dry air ahead of it, I feel at this time, it would be s stretch.

96L CURRENT WIND SHEAR

96L  TPW

96L SAL


Based on analysis of current and forecast steering maps, INVEST 96L should continue on a WNW to NW motion.  The disturbance is positioned as such, that the weakness in the sub-tropical ridge is having an effect on it.  Forecast steering indicates the weakness to become more pronounced during the next 72 hours, as a break between the western and eastern ridge centers. 

EARLY TRACK GUIDANCE

FORECAST STEERING (ARROW INDICATES WEAKNESS LOCATION)

I will continue to monitor this area for any significant changes.

CURRENT AFRICA SATELLITE VIEW (EUMETSAT)

Elsewhere…I am not expecting tropical storm development during the next 5 days.

Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
CoCoRAHS OBSERVER

 

 

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About palmharborforecastcenter

I am a Tropical Forecast meteorologist, providing hurricane forecasts during the Atlantic Hurricane Season. I retired from the U.S. Coast Guard in July of 2001. Meteorology became my passion in high school, and I have continued my educational background in meteorology since 1996, when I undertook the study of Tropical Meteorology. While working toward my degree, I had to unexpectedly withdraw from college due to my oldest sons medical reasons. I do however, meet the educational criteria of the AMS to be recognized as a meteorologist. Studies include, but are not limited to the Navy Aerographers Mate course, Naval METOC meteorology course, Meteorology 2010 Sophomore level course while attending St. Petersburg College, Clearwater, FL., Basic Forecasting course for operational meteorologists from Rapid WX, meteorology institute, a four month meteorological internship, and extensive research on numerous meteorological topics such as the MJO, NAO, satellite imagery interpretation, etc. I have been forecasting Tropical Weather (Tropical Storms and Hurricanes) since 1996, with my main client being three different Coast Guard Commands.
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2 Responses to TROPICAL STORM DON / TROPICAL DISTURBANCE INVEST 96L FORECAST SYNOPSIS…ISSUED JUL. 18, 2017…12:20 P.M. EDT

  1. dellamom says:

    Thank you, Storm. Is there any credible chance that a remnant of Don would make it to the Gulf and develop or just bring a major rain event like we sometimes have?

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