[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 212306
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU MAY 21 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 74W SOUTH OF 13N MOVING WEST NEAR 15
KT. THIS WAVE IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER
MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS.
COMPUTER MODEL GUIDANCE INDICATES THAT THE WAVE COINCIDES WITH
AN AREA OF LOW LEVEL CYCLONIC CIRCULATION...WHICH IS ALSO
ASSOCIATED WITH A 1006 MB SURFACE LOW ALONG THE TROPICAL WAVE IN
N COLOMBIA NEAR 8N74W. SCATTERED MODERATE CONVECTION IS WITHIN
120 NM EITHER SIDE OF THE WAVE AXIS FROM 9N-11N.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 7N12W 3N20W 2N29W CROSSING THE
EQUATOR NEAR 35W EXTENDING TO 1S37W AND INTO NE BRAZIL NEAR
3S42W. SCATTERED MODERATE CONVECTION IS S OF 2N BETWEEN 1W-2W.
SCATTERED MODERATE CONVECTION IS ALSO S OF 5N BETWEEN 10W-22W.
SIMILAR CONVECTION IS S OF 4N BETWEEN 25W-36W.

...DISCUSSION...

GULF OF MEXICO...
A DEEP LAYER TROUGH IS PRESENT ACROSS THE GULF WITH AN UPPER
LEVEL LOW NEAR 27N86W AND AN ASSOCIATED 1006 MB SURFACE LOW NEAR
26N86W. LOW LEVEL CONVERGENCE NEAR THE SURFACE LOW...AS WELL AS
UPPER LEVEL DIFFLUENCE E OF THE UPPER LOW...ARE SUPPORTING
SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE GULF N OF 23N E
OF 87W....INCLUDING THE W FLORIDA PENINSULA. THE TIGHT SURFACE
PRESSURE GRADIENT BETWEEN THE SURFACE LOW AND A SURFACE RIDGE
OVER THE SE CONUS IS SUPPORTING WIND SPEEDS OF 20 TO 30 KT
AROUND THE LOW ACROSS N PORTIONS OF THE MIDDLE AND E GULF. THE
SURFACE LOW IS FORECAST TO MOVE NORTHWESTWARD DURING THE NEXT
DAY AND BE LOCATED NEAR 27N89W AS A 1008 MB SURFACE LOW AT
22/1800 UTC. THE WINDS AROUND THE LOW ARE FORECAST TO BECOME
LIGHTER THIS WEEKEND AS THE PRESSURE GRADIENT AROUND THE LOW
RELAXES. ACROSS THE W GULF...SUBSIDENCE ASSOCIATED WITH
NORTHWESTERLY FLOW ALOFT IS SUPPORTING GENERALLY FAIR WEATHER
CONDITIONS...WITH UPPER LEVEL MOISTURE AND HIGH LEVEL CLOUDS
STREAMING SOUTHEASTWARD. NORTHERLY WINDS UP TO 20 KT ARE
OCCURRING ACROSS THE W GULF.

CARIBBEAN SEA...
NUMEROUS SHOWERS AND THUNDERSTORMS ARE AFFECTING THE NORTH
CENTRAL CARIBBEAN N OF 16N BETWEEN 68W-77W...INCLUDING PORTIONS
OF JAMAICA...HISPANIOLA...AND PUERTO RICO. THIS ACTIVITY IS
BEING SUPPORTED BY STRONG UPPER LEVEL DIFFLUENCE IN MOIST
SOUTHWESTERLY FLOW ALOFT BETWEEN AN UPPER LEVEL TROUGH OVER THE
W CARIBBEAN AND GULF OF MEXICO...AND AN UPPER LEVEL RIDGE ACROSS
THE E CARIBBEAN AND SW NORTH ATLC. THE SHOWERS AND THUNDERSTORMS
ARE ASSOCIATED WITH HEAVY RAINFALL...AS WELL AS MAJOR FLOODING
OVER PORTIONS OF HISPANIOLA. ADDITIONAL SHOWER AND THUNDERSTORM
ACTIVITY IS FORECAST TO AFFECT THE NORTH CENTRAL CARIBBEAN
DURING THE NEXT COUPLE DAYS. ADDITIONALLY...ATMOSPHERIC
INSTABILITY IS RESULTING IN SCATTERED SHOWERS AND THUNDERSTORMS
OVER E CUBA. UPPER LEVEL MOISTURE AND HIGH LEVEL CLOUDS ARE
STREAMING NORTHEASTWARD ACROSS THE W CARIBBEAN AND
EAST-SOUTHEASTWARD ACROSS THE E CARIBBEAN. MEANWHILE...SLIGHT
STRENGTHENING OF A SURFACE RIDGE OVER THE CENTRAL ATLC IS
MAINTAINING LIGHT TO MODERATE TRADES OVER PORTIONS OF THE E
CARIBBEAN...WHERE E TO SE WINDS OF 15 TO 20 KT ARE OCCURRING.
ADDITIONALLY...A TROPICAL WAVE IS MOSTLY INLAND OVER COLOMBIA
AND IS ASSOCIATED WITH SCATTERED MODERATE CONVECTION ACROSS N
COLOMBIA. PLEASE SEE ABOVE FOR FURTHER INFORMATION ON THIS
TROPICAL WAVE.

ATLANTIC OCEAN...
SCATTERED SHOWERS AND THUNDERSTORMS ARE OCCURRING FROM 22N-29N
BETWEEN 74W-79W INCLUDING THE NW BAHAMAS...AS WELL AS S OF 22N
BETWEEN 65W-75W INCLUDING HISPANIOLA AND PUERTO RICO. THIS
ACTIVITY IS BEING SUPPORTED BY STRONG UPPER LEVEL DIFFLUENCE IN
MOIST SOUTHWESTERLY FLOW ALOFT BETWEEN AN UPPER LEVEL TROUGH
OVER THE W CARIBBEAN AND GULF OF MEXICO...AND AN UPPER LEVEL
RIDGE ACROSS THE E CARIBBEAN AND SW NORTH ATLC. THE SHOWERS AND
THUNDERSTORMS ARE ASSOCIATED WITH HEAVY RAINFALL...AS WELL AS
MAJOR FLOODING OVER PORTIONS OF HISPANIOLA. FARTHER TO THE
E...AN UPPER LEVEL TROUGH IS PRESENT WITH AN AXIS EXTENDING FROM
AN UPPER LEVEL LOW NEAR 32N46W TO 30N42W. ATMOSPHERIC
INSTABILITY NEAR THE UPPER LEVEL LOW AND TROUGH...AS WELL AS
UPPER LEVEL DIFFLUENCE IN MOIST SOUTHWESTERLY FLOW ALOFT...ARE
SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS N OF 27N
BETWEEN 38W-49W. ALSO...A SURFACE TROUGH EXTENDS FROM 31N50W TO
A 1016 MB SURFACE LOW NEAR 28N55W TO 23N58W. LOW LEVEL
CONVERGENCE NEAR THESE FEATURES IS SUPPORTING SCATTERED SHOWERS
WITHIN 60 NM EITHER SIDE OF THE SURFACE TROUGH. DURING THE NEXT
DAY...THE 1016 MB SURFACE LOW IS FORECAST TO DISSIPATE. ACROSS
THE E ATLC...A SURFACE RIDGE IS PRESENT WHERE MAINLY ZONAL FLOW
ALOFT IS OCCURRING AND FAIR WEATHER CONDITIONS PERSIST.
HOWEVER...AN UPPER LEVEL TROUGH IS PRESENT N OF 27N E OF 26W
WITH AN ASSOCIATED SURFACE COLD FRONT EXTENDING FROM 25N23W TO
THE CANARY ISLANDS NEAR 28N17W TO 32N15W TO N OF THE DISCUSSION
AREA. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS
WITHIN 60 NM EITHER SIDE OF THIS COLD FRONT. ACROSS THE TROPICAL
ATLC...AN UPPER LEVEL RIDGE IS S OF 11N E OF 49W WITH AN UPPER
LEVEL HIGH NEAR 7N19W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH
THE UPPER LEVEL HIGH AND UPPER LEVEL RIDGE IS ENHANCING THE
CONVECTION ASSOCIATED WITH THE ITCZ.

$$
COHEN


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