[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 181743
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON MAY 18 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 44W/45W S OF 12N TO 3N MOVING W NEAR 10
KT. THIS WAVE IS EMBEDDED WITHIN BROAD SURFACE CYCLONIC FLOW
WITH VISIBLE IMAGERY SHOWING AN INVERTED-V CLOUD PRESENTATION IN
THE LOW-LEVEL CLOUD FIELD S OF 6N BETWEEN 42W-47W. AN EARLIER
ASCAT PASS AROUND 1200 UTC SHOWED 15-20 KT WINDS IN THE VICINITY
OF THE WAVE AXIS WITH ISOLATED MODERATE CONVECTION FROM 1N-5N
BETWEEN 43W-47W.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 5N10W 1N20W CROSSING THE EQUATOR
NEAR 24W EXTENDING TO 2S38W AND INTO NE BRAZIL NEAR 1S46W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 2N-6N
BETWEEN 10W-17W. SIMILAR CONVECTION IS S OF 5N BETWEEN 19W-26W.

...DISCUSSION...

GULF OF MEXICO...
A DEEP LAYER TROUGH OVER THE ERN CONUS IS ASSOCIATED WITH A
SURFACE STATIONARY FRONT OVER THE FLORIDA PENINSULA AND E GULF
THAT AT 1500 UTC EXTENDS FROM TITUSVILLE FLORIDA TO TAMPA BAY
AND ALONG 27N86W 24N89W CLIPPING THE NW YUCATAN PENINSULA AND
ALONG THE COAST TO 19N92W. ALSO...A SURFACE TROUGH IS LOCATED TO
THE E OF THE FRONT AND EXTENDS FROM NEAR 28N84W TO 22N85W. LOW
LEVEL CONVERGENCE NEAR THE STATIONARY FRONT AND SURFACE TROUGH
IS SUPPORTING NUMEROUS SHOWERS AND SCATTERED TSTMS OVER THE GULF
N OF 24N E OF 88W TO OVER THE FLORIDA PENINSULA AND INTO THE W
ATLC. THIS ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE
BETWEEN THE AFOREMENTIONED DEEP TROUGH AND AN UPPER LEVEL RIDGE
OVER THE SW GULF. THE FRONT IS EXPECTED TO GRADUALLY WEAKEN
ACROSS THE GULF DURING THE NEXT DAY...AS MANY OF THE GLOBAL
MODELS ARE SHOWING LOW PRESSURE DEVELOPING OVER THE SW NORTH
ATLC AND SE GULF...EITHER EXTRATROPICAL OR SUBTROPICAL...AND
MOVE GENERALLY N. THE DEVELOPMENT AND TRACK OF THE LOW REMAINS
UNCERTAIN...THOUGH COMPUTER MODELS SUGGEST THAT WINDS WILL
INCREASE AROUND THE LOW.

CARIBBEAN SEA...
SCATTERED SHOWERS AND TSTMS ARE AFFECTING PORTIONS OF THE NORTH
CENTRAL CARIBBEAN N OF 15N BETWEEN 68W-77W...INCLUDING E CUBA...
HISPANIOLA AND THE WINDWARD PASSAGE. THIS ACTIVITY IS BEING
SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A SURFACE TROUGH THAT
EXTENDS FROM EXUMA SOUND IN THE BAHAMAS ACROSS ERN CUBA TO
16N76W. THE ACTIVITY IS ALSO BEING SUPPORTED BY MIDDLE TO UPPER
LEVEL DIFFLUENCE BETWEEN AN UPPER RIDGE OVER THE SW NORTH ATLC
AND AN UPPER TROUGH OVER THE CENTRAL CARIBBEAN. DURING THE NEXT
DAY...A SURFACE LOW IS FORECAST TO DEVELOP ALONG THE SURFACE
TROUGH AND MOVE N OF THE CARIBBEAN BY TUESDAY. UPPER LEVEL
DIVERGENCE AND ATMOSPHERIC INSTABILITY ASSOCIATED WITH THE UPPER
TROUGH OVER THE CENTRAL CARIBBEAN IS ALSO SUPPORTING SCATTERED
SHOWERS OVER THE NE CARIBBEAN N OF 16N...IMPACTING PUERTO
RICO...THE VIRGIN AND LEEWARD ISLANDS.

ATLANTIC OCEAN...
AN OCCLUDED 1009 MB SURFACE LOW IS QUASI-STATIONARY NEAR 32N52W.
AN ASSOCIATED SURFACE STATIONARY FRONT EXTENDS FROM 30N45W TO
25N46W TO 22N50W W-SW TO NEAR BARBUDA. LOW-LEVEL CONVERGENCE IS
SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS ALONG AND WITHIN
250 NM E OF THE SURFACE FRONT N OF 22N. S OF 22N...SCATTERED
SHOWERS ARE WITHIN 60 NM EITHER SIDE OF THE FRONT. A SURFACE
TROUGH IS ALSO ANALYZED TO THE W OF THE STATIONARY FRONT AND
EXTENDS FROM 31N49W TO 28N49W TO 24N57W. LOW LEVEL CONVERGENCE
IS SUPPORTING SCATTERED SHOWERS WITHIN 30 NM EITHER SIDE OF THIS
SURFACE TROUGH. ALL OF THIS SHOWER AND THUNDERSTORM ACTIVITY IS
BEING ENHANCED BY UPPER LEVEL DIFFLUENCE IN THE ERN SEMICIRCLE
OF AN UPPER LOW NEAR 32N52W. FARTHER TO THE W...A SURFACE RIDGE
EXTENDS SW FROM A SURFACE HIGH PRESSURE CENTERED NW OF BERMUDA.
SUBSIDENCE AND ATMOSPHERIC STABILITY ASSOCIATED WITH AN UPPER
RIDGE OVER THE SW NORTH ATLC...IS SUPPORTING GENERALLY FAIR
WEATHER CONDITIONS BETWEEN 57W-73W. HOWEVER...MOIST SELY LOW
LEVEL FLOW OVER PORTIONS OF THE SW NORTH ATLC IS SUPPORTING
SCATTERED SHOWERS AND TSTMS W OF 72W ALL FOCUSED ON A STATIONARY
FRONT THAT ENTERS THE REGION NEAR 32N77W EXTENDING SW TO NEAR
TITUSVILLE FLORIDA. ADDITIONALLY...SCATTERED SHOWERS AND TSTMS
ASSOCIATED WITH THE SURFACE TROUGH OVER THE CENTRAL CARIBBEAN
ACROSS ERN CUBA TO 23N76W ARE MOVING NWD INTO THE W ATLC
IMPACTING THE WINDWARD PASSAGE...TURKS AND CAICOS ISLANDS AS
WELL AS THE BAHAMAS. DURING THE NEXT DAY...MANY OF THE GLOBAL
MODELS ARE SHOWING LOW PRESSURE DEVELOPING OVER THE SW NORTH
ATLC AND SE GULF OF MEXICO...EITHER EXTRATROPICAL OR
SUBTROPICAL...AND MOVING GENERALLY NWD. THE PRESSURE GRADIENT
AROUND THE LOW IS FORECAST TO RESULT IN GALE CONDITIONS N OF 29N
W OF 76W EARLY TUESDAY THROUGH WEDNESDAY. ACROSS THE E ATLC...A
SURFACE RIDGE IS PRESENT WHERE MAINLY ZONAL FLOW ALOFT IS
OBSERVED AND FAIR WEATHER CONDITIONS PERSIST. ACROSS THE
TROPICAL ATLC...AN UPPER LEVEL RIDGE IS PRESENT S OF 12N E OF
58W WITH UPPER LEVEL HIGHS CENTERED NEAR 6N26W AND 5N48W. UPPER
LEVEL DIVERGENCE ASSOCIATED WITH THE UPPER LEVEL HIGHS AND RIDGE
IS ENHANCING THE CONVECTION ASSOCIATED WITH THE ITCZ.

$$
HUFFMAN




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