[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 232341
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU JUL 23 2009

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...TROPICAL WAVES...

A TROPICAL WAVE EXTENDS ALONG 19N29W TO 09N27W MOVING W 10-15
KT. SATELLITE IMAGES INDICATE A BROAD AREA OF LOW-LEVEL
CYCLONIC TURNING ABOUT THE WAVE AXIS WITH CLOUD MOTIONS
SUGGESTING A WEAK LOW NEAR 14N28W. AN EARLIER ASCAT PASS
INDICATED THAT THE CYCLONIC TURNING IS AT THE SFC...THOUGH WINDS
ARE GENERALLY WEAK. CONVECTION IS MINIMAL IN THE VICINITY OF THE
WAVE SUPPRESSED BY SAHARAN DUST.

A TROPICAL WAVE IS ALONG 62W/63W S OF 18N MOVING W NEAR 25 KT.
UPPER AIR SOUNDINGS FROM CAYENNE SUGGEST THAT THIS WAVE PASSED
THE STATION AROUND 22/1200 UTC. VISIBLE SATELLITE IMAGERY AND
TOTAL PRECIPITABLE WATER IMAGES INDICATE A SLIGHT INVERTED
V-SHAPE OVER THE E CARIBBEAN. UPPER DIFFLUENCE IS AIDING IN THE
DEVELOPMENT OF SCATTERED SHOWERS OVER THE LESSER ANTILLES AND
ATLC WATERS FROM 13N-16N BETWEEN 55W-62W.

A TROPICAL WAVE IS ALONG 74W/75W S OF 20N MOVING W NEAR 20 KT.
SATELLITE IMAGES SHOW LITTLE EVIDENCE OF THIS WAVE AT THE
MOMENT. THE CURRENT POSITION IS BASED ON 24-H 2-3 MB PRESSURE
FALLS OVER THE N PORTION OF COLOMBIA...WHICH AGREES WELL WITH
FORWARD EXTRAPOLATION.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 11N14W 10N35W 10N63W. SCATTERED
MODERATE CONVECTION IS WITHIN 240 NM OF THE AXIS E OF 20W.
SCATTERED MODERATE CONVECTION IS FROM 10N-12N BETWEEN 37W-51W.

...DISCUSSION...

GULF OF MEXICO...
UPPER LEVEL DIFFLUENCE AND MOISTURE IN WESTERLY FLOW ALOFT
COMBINED WITH LOW-LEVEL CONVERGENCE ALONG A SFC TROUGH ARE
SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS OVER N OF 28N
BETWEEN 86W-93W. SCATTERED SHOWERS AND TSTMS ARE OVER S FLORIDA
ENHANCED BY THE TAIL END OF A SFC TROUGH THAT EXTENDS FROM A LOW
OFF THE MID-ATLANTIC COAST. ELSEWHERE...DEEP LAYER DRY AIR AND
SFC RIDGING IS PROMOTING FAIR WEATHER. THE SURFACE RIDGE IS
FORECAST TO GRADUALLY SHIFT EASTWARD THROUGH THE WEEKEND WITH
INCREASING SE RETURN FLOW ACROSS THE W GULF BY LATE IN THE
WEEKEND AND EARLY NEXT WEEK.

CARIBBEAN SEA...
A BROAD UPPER LEVEL ANTICYCLONE IS OVER THE W CARIBBEAN...
CENTERED OVER THE GULF OF HONDURAS. UPPER LEVEL DIFFLUENCE
ASSOCIATED WITH THIS ANTICYCLONE AND LOW-LEVEL SPEED CONVERGENCE
ARE SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS OVER PORTIONS
OF COSTA RICA...NICARAGUA...AND HONDURAS. UPPER LEVEL DIFFLUENCE
IS ALSO SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS OVER CUBA
AND JAMAICA...WHERE ATMOSPHERIC INSTABILITY IS BEING ENHANCED BY
DIURNAL HEATING. ACROSS THE E CARIBBEAN...SCATTERED SHOWERS AND
ISOLATED TSTMS ARE AFFECTING THE LESSER ANTILLES ENHANCED BY A
TROPICAL WAVE. FAIR WEATHER EXISTS ACROSS THE CENTRAL CARIBBEAN
SUPPORTING BY DRY AIR ALOFT.

ATLANTIC OCEAN...
A MID-UPPER LEVEL TROUGH IS OVER THE W ATLC. THIS FEATURE IS
ASSOCIATED WITH A SURFACE TROUGH EXTENDING FROM S FLORIDA TO
32N72W. DIFFLUENCE ALOFT...BETWEEN THE UPPER LEVEL TROUGH AND AN
UPPER LEVEL RIDGE...AND LOW-LEVEL CONVERGENCE ARE SUPPORTING
NUMEROUS SHOWERS AND THUNDERSTORMS N OF 26N BETWEEN 70W-75W.
ISOLATED SHOWERS AND TSTMS ARE ELSEWHERE W OF 70W. THE SURFACE
PRESSURE GRADIENT E OF THE TROUGH IS SUPPORTING S TO SW WINDS OF
20 KT N OF 28N BETWEEN 70W AND 73W. FARTHER TO THE E...
SUBSIDENCE ASSOCIATED WITH A DEEP LAYER RIDGE IS RESULTING IN
GENERALLY FAIR WEATHER ACROSS MUCH OF THE CENTRAL AND E ATLC.
ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER TROUGH IS
SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS FROM 11N-17N
BETWEEN 55W-61W.

$$
CANGIALOSI/COHEN





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