[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 172312
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN MAY 17 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 EXTENDS FROM 11N40W TO 1N43W 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. COMPUTER MODEL GUIDANCE INDICATES THAT THE
WAVE COINCIDES WITH AN AREA OF LOW LEVEL CYCLONIC CIRCULATION.
SCATTERED MODERATE CONVECTION IS OCCURRING WITHIN 180 NM E OF
THE WAVE S OF 4N.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 7N11W 3N17W CROSSING THE EQUATOR
NEAR 22W EXTENDING TO 2S30W 3S35W AND INTO NE BRAZIL NEAR 3S46W.
SCATTERED MODERATE CONVECTION IS S OF 3N BETWEEN 13W-20W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS S OF 3N BETWEEN
21W-29W.

...DISCUSSION...

GULF OF MEXICO...
A DEEP LAYER TROUGH OVER THE SOUTH CENTRAL CONUS IS ASSOCIATED
WITH A SURFACE STATIONARY FRONT OVER THE W GULF THAT EXTENDS
FROM SOUTH CENTRAL LOUISIANA NEAR 29N91W TO 26N95W TO THE COAST
OF MEXICO NEAR 22N98W. ALSO...A SURFACE TROUGH IS LOCATED TO THE
E OF THE FRONT AND EXTENDS FROM S MISSISSIPPI NEAR 30N89W TO N
OF THE YUCATAN PENINSULA NEAR 22N89W. LOW LEVEL CONVERGENCE NEAR
THE SURFACE FRONT AND SURFACE TROUGH IS SUPPORTING SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS OVER THE GULF N OF 26N
BETWEEN 86W-95W...WITH SCATTERED SHOWERS S OF 23N W OF 91W.
ADDITIONALLY...RELATIVELY UNSTABLE ATMOSPHERIC CONDITIONS
ASSOCIATED WITH MOIST SOUTHEASTERLY FLOW OVER THE E GULF ARE
SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS FROM 23N TO 29N E
OF 84W INCLUDING THE W FLORIDA PENINSULA...THE FLORIDA
KEYS...THE STRAITS OF FLORIDA...AND W CUBA. ALL OF THE SHOWER
AND THUNDERSTORM 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 MOVE
SOUTHEASTWARD AS A COLD FRONT THROUGH TUESDAY. ALSO... DURING
THE NEXT DAY...MANY OF THE GLOBAL MODELS ARE SHOWING LOW
PRESSURE DEVELOPING OVER THE N CENTRAL CARIBBEAN...EITHER
EXTRATROPICAL OR SUBTROPICAL...AND MOVING GENERALLY N. THE
DEVELOPMENT AND TRACK OF THE LOW REMAIN UNCERTAIN...THOUGH
COMPUTER MODELS SUGGEST THAT WINDS WILL INCREASE AROUND THE LOW.

CARIBBEAN SEA...
NUMEROUS SHOWERS AND THUNDERSTORMS ARE AFFECTING PORTIONS OF THE
NORTH CENTRAL CARIBBEAN N OF 16N BETWEEN 71W-79W...INCLUDING
JAMAICA...E CUBA...AND W HISPANIOLA. THIS ACTIVITY IS BEING
SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A SURFACE TROUGH THAT
EXTENDS FROM E CUBA NEAR 20N76W TO 16N76W. THE ACTIVITY IS ALSO
BEING SUPPORTED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER RIDGE
OVER THE SW NORTH ATLC AND AN UPPER TROUGH OVER THE S CARIBBEAN.
DURING THE NEXT DAY...A SURFACE LOW IS FORECAST TO DEVELOP ALONG
THE SURFACE TROUGH AND MOVE N OF THE CARIBBEAN MONDAY NIGHT.
UPPER LEVEL DIVERGENCE AND ATMOSPHERIC INSTABILITY ASSOCIATED
WITH THE UPPER TROUGH OVER THE S CARIBBEAN IS ALSO SUPPORTING
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS OVER THE SW
CARIBBEAN S OF 10N AND SCATTERED SHOWERS OVER THE E CARIBBEAN
FROM 14N TO 17N BETWEEN 63W-69W. ADDITIONALLY...ATMOSPHERIC
INSTABILITY IS RESULTING IN SCATTERED SHOWERS AND THUNDERSTORMS
OVER W CUBA...IMPACTING THE ADJACENT COASTAL WATERS. ALSO...
SCATTERED SHOWERS ARE OCCURRING WITHIN 90 NM EITHER SIDE OF A
SURFACE TROUGH OVER THE NW CARIBBEAN THAT EXTENDS FROM 19N85W TO
16N85W. MEANWHILE...SURFACE HIGH PRESSURE CENTERED W OF BERMUDA
IS MAINTAINING 15-20 KT EASTERLY TRADE WINDS ACROSS MUCH OF THE
E CARIBBEAN.

ATLANTIC OCEAN...
AN OCCLUDED 1006 MB SURFACE LOW IS NEARLY STATIONARY NEAR
32N53W. AN ASSOCIATED SURFACE COLD FRONT EXTENDS FROM 32N46W TO
27N47W TO 24N49W AND CONTINUING SOUTHWESTWARD AS A STATIONARY
FRONT TO 19N56W. FROM 19N56W...THE BOUNDARY WEAKENS TO A SURFACE
TROUGH AND EXTENDS SW TO 16N59W. LOW LEVEL CONVERGENCE IS
SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ALONG
AND WITHIN 300 NM E OF THE SURFACE FRONTS AND SURFACE TROUGH. A
SURFACE TROUGH IS ALSO PRESENT TO THE W OF THE COLD AND
STATIONARY FRONTS AND EXTENDS FROM 30N48W TO 27N52W TO 27N58W.
LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 60
NM EITHER SIDE OF THIS SURFACE TROUGH. ALL OF THIS SHOWER AND
THUNDERSTORM ACTIVITY IS BEING ENHANCED BY UPPER LEVEL
DIFFLUENCE NEAR AN UPPER TROUGH THAT EXTENDS FROM AN UPPER LOW
NEAR 32N52W TO 28N49W TO 26N49W. FARTHER TO THE W...A SURFACE
RIDGE EXTENDS SOUTHWESTWARD FROM SURFACE HIGH PRESSURE CENTERED
W OF BERMUDA. SUBSIDENCE ASSOCIATED WITH THIS SURFACE
RIDGE...COMBINED WITH ATMOSPHERIC STABILITY ASSOCIATED WITH AN
UPPER RIDGE OVER THE SW NORTH ATLC...IS SUPPORTING GENERALLY
FAIR WEATHER CONDITIONS ACROSS MUCH OF THE SW NORTH ATLC.
HOWEVER...MOIST SOUTHEASTERLY LOW LEVEL FLOW OVER PORTIONS OF
THE SW NORTH ATLC IS SUPPORTING SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS S OF 25N W OF 78W. ADDITIONALLY...NUMEROUS SHOWERS
AND THUNDERSTORMS ASSOCIATED WITH THE SURFACE TROUGH OVER THE
NORTH CENTRAL CARIBBEAN ARE MOVING NORTHWARD INTO THE SW N
ATLC...AFFECTING LOCATIONS S OF 22N BETWEEN 71W-79W...INCLUDING
PORTIONS OF E CUBA AND W HISPANIOLA. DURING THE NEXT DAY...MANY
OF THE GLOBAL MODELS ARE SHOWING LOW PRESSURE DEVELOPING OVER
THE N CENTRAL CARIBBEAN...EITHER EXTRATROPICAL OR SUBTROPICAL...
AND MOVING GENERALLY N INTO THE SW NORTH ATLC. THE PRESSURE
GRADIENT AROUND THE LOW IS FORECAST TO RESULT IN GALE CONDITIONS
N OF 28N W OF 75W MONDAY NIGHT THROUGH WEDNESDAY. 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 11N E OF
58W WITH UPPER LEVEL HIGHS CENTERED NEAR 6N46W AND 5N25W. 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 THAT EXTENDS FROM 11N40W TO 1N43W.

$$
COHEN




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