[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 182325
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2245 UTC.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 45W/46W S OF 12N TO 2N MOVING W NEAR 10
KT. THIS WAVE IS EMBEDDED WITHIN A BROAD INVERTED-V STRUCTURE IN
THE LOW-LEVEL CLOUD COVERAGE...AND IS ASSOCIATED WITH A MAXIMUM
IN DEEP LAYER MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT
FROM CIMSS. SCATTERED MODERATE CONVECTION IS OCCURRING WITHIN
90 NM EITHER SIDE OF THE WAVE S OF 6N.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 5N9W 2N18W CROSSING THE EQUATOR
NEAR 28W EXTENDING TO 2S36W AND INTO NE BRAZIL NEAR 3S45W.
SCATTERED MODERATE CONVECTION IS S OF 2N BETWEEN 1W-3W.
SCATTERED MODERATE CONVECTION IS ALSO S OF 2N BETWEEN 7W-9W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS S OF 6N BETWEEN
15W-21W. SCATTERED MODERATE CONVECTION IS S OF 2N BETWEEN
26W-29W.

...DISCUSSION...

GULF OF MEXICO...
A DEEP LAYER TROUGH OVER THE E CONUS AND E GULF IS ASSOCIATED
WITH A SURFACE COLD OVER THE E GULF THAT EXTENDS FROM THE SOUTH
FLORIDA PENINSULA NEAR 26N82W TO 26N83W. FARTHER TO THE SW...A
NEWLY-DEVELOPED 1010 MB SURFACE LOW IS LOCATED NEAR 25N85W...
WITH A SURFACE TROUGH EXTENDING FROM 26N84W TO THE SURFACE LOW
TO 22N85W. THIS SURFACE LOW IS LOCATED BENEATH THE SOUTHWESTERN
PORTION OF THE DEEP LAYER TROUGH THAT EXTENDS INTO THE E GULF.
LOW LEVEL CONVERGENCE NEAR THE LOW...TROUGH...AND COLD FRONT IS
SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS OVER THE GULF
FROM 23N-29N E OF 87W...INCLUDING THE CENTRAL AND SOUTH FLORIDA
PENINSULA...THE STRAITS OF FLORIDA...THE FLORIDA KEYS...AND W
CUBA. THIS SHOWER AND THUNDERSTORM ACTIVITY IS BEING ENHANCED BY
UPPER LEVEL DIFFLUENCE BETWEEN THE AFOREMENTIONED DEEP TROUGH
AND AN UPPER LEVEL RIDGE OVER THE SW NORTH ATLC. DURING THE NEXT
DAY...THE SURFACE LOW IS FORECAST TO MOVE EASTWARD AND BE
LOCATED OVER THE FLORIDA KEYS NEAR 25N81W AS A 1009 MB SURFACE
LOW AT 19/1800 UTC. HOWEVER...THE FUTURE DEVELOPMENT AND TRACK
OF THE LOW REMAIN UNCERTAIN...THOUGH COMPUTER MODEL GUIDANCE
SUGGESTS THAT WINDS WILL INCREASE AROUND THE LOW...WHICH WILL
AFFECT PORTIONS OF THE GULF OF MEXICO. ACROSS THE WEST GULF...
DEEP LAYER DRY AIR...AS WELL AS SUBSIDENCE WITH CONFLUENT UPPER
LEVEL NORTHWESTERLY FLOW...ARE RESULTING IN GENERALLY FAIR
WEATHER CONDITIONS. ALSO...N TO NE SURFACE WINDS ARE OCCURRING
ACROSS THE W GULF...WITH WIND SPEEDS UP TO 25 KT ACROSS PORTIONS
OF THE NW GULF.

CARIBBEAN SEA...
SCATTERED SHOWERS AND THUNDERSTORMS ARE AFFECTING PORTIONS OF
THE N CARIBBEAN N OF 17N BETWEEN 67W-78W...INCLUDING JAMAICA...
HISPANIOLA...AND E CUBA. THIS ACTIVITY IS BEING SUPPORTED BY
ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER LEVEL TROUGH
OVER THE CARIBBEAN WITH AN AXIS EXTENDING FROM 18N72W TO 13N73W
TO 11N74W. ADDITIONALLY...ATMOSPHERIC INSTABILITY IS RESULTING
IN SCATTERED SHOWERS AND THUNDERSTORMS OVER HONDURAS...W CUBA
AND E PORTIONS OF THE YUCATAN PENINSULA...IMPACTING THE ADJACENT
COASTAL WATERS...WITH SCATTERED SHOWERS AND THUNDERSTORMS ALSO
OVER PANAMA AND COSTA RICA. UPPER LEVEL MOISTURE AND HIGH LEVEL
CLOUDS ARE STREAMING SOUTHEASTWARD ACROSS THE W CARIBBEAN AND
NORTHEASTWARD ACROSS THE E CARIBBEAN. MEANWHILE...SURFACE HIGH
PRESSURE CENTERED NW OF BERMUDA IS MAINTAINING 15-20 KT E WINDS
PORTIONS OF THE E CARIBBEAN.

ATLANTIC OCEAN...
SCATTERED SHOWERS AND THUNDERSTORMS ARE OCCURRING S OF 24N
BETWEEN 67W-80W...INCLUDING E CUBA...THE SE BAHAMAS...AND THE
ADJACENT WATERS OF THE SW NORTH ATLC AS WELL AS HISPANIOLA. THIS
ACTIVITY IS BEING SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A 1011
MB SURFACE LOW NE OF CUBA NEAR 22N76W AND A TROUGH EXTENDING
FROM 23N74W TO THE SURFACE LOW TO E CUBA NEAR 21N77W. THIS
ACTIVITY IS ALSO BEING SUPPORTED BY UPPER LEVEL DIFFLUENCE
BETWEEN AN UPPER LEVEL RIDGE OVER THE SW NORTH ATLC AND AN UPPER
LEVEL TROUGH ACROSS THE CARIBBEAN. SLOW DEVELOPMENT OF THIS
SYSTEM IS POSSIBLE DURING THE NEXT DAY OR TWO AS IT MOVES
GENERALLY NORTHWARD AT 10 TO 15 MPH. THE LOW IS FORECAST TO BE
LOCATED NEAR 26N76W AS A 1010 MB LOW AT 19/1800 UTC. DURING THE
NEXT 48 HOURS...THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...
OF THIS SYSTEM BECOMING A TROPICAL CYCLONE. IF NECESSARY...AN
AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT WILL INVESTIGATE THE
SYSTEM ON TUESDAY. ALSO...THE PRESSURE GRADIENT AROUND THE LOW
IS FORECAST TO RESULT IN GALE CONDITIONS N OF 27N W OF 75W
TONIGHT THROUGH WEDNESDAY.

ALSO ACROSS THE SW NORTH ATLC...THE DEEP LAYER TROUGH OVER THE E
CONUS AND E GULF OF MEXICO IS SUPPORTING A COLD FRONT THAT
EXTENDS FROM 32N77W TO 29N79W TO 28N80W. GALE CONDITIONS ARE
FORECAST TO DEVELOP N OF THE FRONT BEGINNING AT 19/0000 UTC. LOW
LEVEL CONVERGENCE NEAR THE COLD FRONT IS SUPPORTING SCATTERED
SHOWERS AND THUNDERSTORMS OVER THE SW NORTH ATLC FROM 24N-30N W
OF 75W...INCLUDING PORTIONS OF W CUBA...THE NW BAHAMAS AND THE
CENTRAL AND S FLORIDA PENINSULA. E OF THE FRONT...A SURFACE
RIDGE EXTENDS SOUTHWESTWARD FROM SURFACE HIGH PRESSURE CENTERED
NW OF BERMUDA. SUBSIDENCE ASSOCIATED WITH THIS SURFACE
RIDGE...AS WELL AS ATMOSPHERIC STABILITY ASSOCIATED WITH THE
UPPER RIDGE OVER THE SW NORTH ATLC...ARE SUPPORTING GENERALLY
FAIR WEATHER CONDITIONS.

FARTHER TO THE E...AN OCCLUDED 1010 MB SURFACE LOW IS LOCATED
NEAR 32N53W. AN ASSOCIATED SURFACE OCCLUDED FRONT EXTENDS FROM
32N46W TO 31N46W AND THEN SOUTHWESTWARD AS A STATIONARY FRONT
FROM 31N46W TO 23N48W TO 19N56W TO 18N63W. LOW LEVEL CONVERGENCE
IS SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ALONG
AND WITHIN 120 NM E OF THE FRONTS. THIS SHOWER AND THUNDERSTORM
ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE NEAR AN
UPPER TROUGH THAT EXTENDS FROM AN UPPER LOW NEAR 32N51W TO
31N45W TO 27N42W. ACROSS THE E ATLC...A SURFACE RIDGE IS PRESENT
WHERE MAINLY ZONAL FLOW ALOFT IS OCCURRING AND FAIR WEATHER
CONDITIONS PERSIST.

ACROSS THE TROPICAL ATLC...AN UPPER LEVEL RIDGE IS PRESENT S OF
13N E OF 58W WITH UPPER LEVEL HIGHS CENTERED NEAR 4N48W AND
5N27W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE UPPER LEVEL
HIGHS AND UPPER LEVEL RIDGE IS ENHANCING THE CONVECTION
ASSOCIATED WITH THE ITCZ AND WITH THE TROPICAL WAVE ALONG
45W/46W S OF 12N TO 2N.

$$
COHEN




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