[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 312318
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI JUL 31 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 HAS BEEN ADDED TO THE SURFACE ANALYSIS OVER THE
TROPICAL E ATLC AS OF 31/1800 UTC. THIS TROPICAL WAVE IS ALONG
24W S OF 18N MOVING W 10-15 KT. UPPER AIR DATA FROM DAKAR
SENEGAL NEAR 15N18W INDICATE THAT THE ANOMALOUS WINDS BELOW 700
MB HAD A NORTHERLY COMPONENT PRIOR TO 31/0000 UTC...AND THEN
ATTAINED A SOUTHERLY COMPONENT AFTER 31/0000 UTC...SUGGESTING
THAT THE WAVE LIKELY PASSED DAKAR AROUND 31/0000 UTC. THIS
TROPICAL WAVE IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER
MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM
CIMSS. SATELLITE-DERIVED WINDS INDICATE CYCLONIC CURVATURE IN
THE 800-600 MB FLOW NEAR THIS WAVE...AND RECENT SATELLITE
IMAGERY INDICATES THAT THIS WAVE COINCIDES WITH A LOW/MID-LEVEL
CYCLONIC CIRCULATION CENTER NEAR 13N24W. SCATTERED MODERATE
CONVECTION IS FROM 10N-14N BETWEEN 24W-26W.

A TROPICAL WAVE OVER THE TROPICAL ATLC IS ALONG 48W/49W S OF 25N
MOVING W 25-30 KT. RECENT SATELLITE IMAGERY INDICATES THAT THIS
WAVE COINCIDES WITH AN INVERTED-V PATTERN IN THE COVERAGE OF LOW
LEVEL CLOUDS. SATELLITE-DERIVED WINDS INDICATE CYCLONIC
CURVATURE IN THE FLOW WITHIN THE 950-800 MB LAYER IN THE
VICINITY OF THIS WAVE. THIS WAVE COINCIDES WITH A MAXIMUM IN
DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER
IMAGERY FROM CIMSS. LOW/MID-LEVEL DRY SAHARAN AIR IS INHIBITING
DEEP CONVECTION NEAR THE NORTHERN PORTIONS OF THE WAVE. ACROSS
THE S PORTIONS OF THE WAVE...SCATTERED MODERATE CONVECTION IS
FROM 6N-10N BETWEEN 42W-50W...WHICH IS BEING ENHANCED BY LOW
LEVEL CONVERGENCE NEAR THE ITCZ.

A TROPICAL WAVE OVER THE CENTRAL AND SW CARIBBEAN EXTENDS FROM
19N73W TO 13N77W TO THE E PACIFIC REGION NEAR 1N79W MOVING W
NEAR 25 KT. THE LOCATION OF THIS WAVE HAS BEEN RELOCATED
SUBSTANTIALLY WESTWARD OF ITS LOCATION AT 31/1200 UTC...WHICH
WAS ALONG 71W S OF 20N. THE NEW LOCATION OF THIS WAVE COINCIDES
WITH AN AXIS OF CYCLONIC MOTION OF LOW LEVEL CLOUDS BASED ON
RECENT VISIBLE SATELLITE IMAGERY. THIS NEW LOCATION ALSO
COINCIDES WITH A WESTWARD-EXTRAPOLATED MAXIMUM IN LOW LEVEL
CYCLONIC CIRCULATION BASED ON THE ASCAT PASS AROUND 31/1500 UTC.
THIS WAVE IS EMBEDDED WITHIN A BROAD MAXIMUM IN DEEP LAYER
MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM
CIMSS. SCATTERED MODERATE CONVECTION IS FROM 17N-20N BETWEEN
76W-80W INCLUDING PORTIONS OF E CUBA. SCATTERED MODERATE
CONVECTION IS ALSO FROM 9N-11N BETWEEN 79W-82W.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 14N17W 11N28W 11N40W 10N53W
9N51W. SCATTERED MODERATE CONVECTION IS FROM 10N-12N BETWEEN
26W-28W. SCATTERED MODERATE CONVECTION IS ALSO FROM 8N-10N
BETWEEN 42W-44W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL RIDGE EXTENDS EASTWARD FROM AN UPPER LEVEL HIGH
OVER NE MEXICO ACROSS THE N GULF OF MEXICO. UPPER LEVEL
DIFFLUENCE BETWEEN THIS UPPER LEVEL RIDGE AND AN UPPER LEVEL
TROUGH OVER THE E UNITED STATES IS SUPPORTING SCATTERED SHOWERS
AND THUNDERSTORMS OVER THE N GULF N OF 29N BETWEEN 84W-90W.
ADDITIONALLY...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE
OCCURRING FROM 26N-28N E OF 85W...WHICH ARE RESULTING FROM
ATMOSPHERIC INSTABILITY CAUSED BY DIURNAL HEATING OVER THE
FLORIDA PENINSULA. ACROSS MUCH OF THE CENTRAL AND SW GULF...DEEP
LAYER DRY AIR AND SUBSIDENCE IN NORTHEASTERLY FLOW ALOFT S OF
THE AFOREMENTIONED UPPER LEVEL RIDGE ARE SUPPORTING GENERALLY
FAIR WEATHER. THIS SUBSIDENCE IS ALSO SUPPORTING A SURFACE RIDGE
ACROSS THE N GULF. THE INCREASED PRESSURE GRADIENT BETWEEN THIS
SURFACE RIDGE AND LOWER SURFACE PRESSURE OVER MEXICO IS
SUPPORTING SE WINDS OF 15 TO 20 KT ACROSS THE SW GULF.

CARIBBEAN SEA...
LOW LEVEL CONVERGENCE DUE TO REGIONAL VARIATIONS IN LOW LEVEL
WIND SPEED OVER THE W CARIBBEAN IS SUPPORTING SCATTERED SHOWERS
AND THUNDERSTORMS OVER THE W CENTRAL CARIBBEAN FROM 11N-16N
BETWEEN 81W-84W...INCLUDING PORTIONS OF E HONDURAS AND E
NICARAGUA. TO THE E...SCATTERED MODERATE CONVECTION IS PRESENT
OVER THE CENTRAL AND SW CARIBBEAN AND IS ASSOCIATED WITH A
TROPICAL WAVE DISCUSSED IN THE TROPICAL WAVES SECTION ABOVE.
ACROSS THE E CARIBBEAN...DEEP LAYER DRY AIR...INCLUDING
LOW/MID-LEVEL DRY SAHARAN AIR...IS SUPPORTING GENERALLY FAIR
WEATHER. FRESH TO STRONG TRADE WINDS ARE PRESENT ACROSS MUCH OF
THE CENTRAL AND S CARIBBEAN TO THE S OF A SURFACE RIDGE OVER THE
CENTRAL ATLC. THE STRONGEST WINDS ARE FOUND NEAR THE COAST OF
COLOMBIA...WHERE NE TO E WINDS ARE FORECAST TO INCREASE TO
BETWEEN 25 AND 30 KT TONIGHT.

ATLANTIC OCEAN...
ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER LEVEL TROUGH
OVER THE SW NORTH ATLC IS SUPPORTING SCATTERED SHOWERS AND
THUNDERSTORMS FROM 23N-26N BETWEEN 78W-80W. FARTHER TO THE
E...SUBSIDENCE IS OCCURRING NEAR A BROAD SURFACE RIDGE AND IS
RESULTING IN GENERALLY FAIR WEATHER ACROSS MUCH OF THE CENTRAL
AND E ATLC. THIS BROAD SURFACE RIDGE IS ASSOCIATED WITH A 1029
MB SURFACE HIGH NEAR 35N53W AND A 1028 MB SURFACE HIGH NEAR
37N41W. HOWEVER...ATMOSPHERIC INSTABILITY NEAR AN UPPER LEVEL
LOW CENTERED NEAR 32N58W IS SUPPORTING SCATTERED SHOWERS N OF
30N BETWEEN 56W-59W. ANOTHER UPPER LEVEL LOW IS CENTERED NEAR
28N41W WITH ATMOSPHERIC INSTABILITY SUPPORTING SCATTERED SHOWERS
FROM 27N-29N BETWEEN 38W-41W. ALSO...AN UPPER LEVEL LOW IS
CENTERED OVER THE E ATLC NEAR 24N23W AND IS ASSOCIATED WITH A
SURFACE TROUGH EXTENDING FROM 22N27W TO 19N21W TO 17N14W. THIS
SURFACE TROUGH IS LOCATED TO THE N OF THE TROPICAL WAVE ALONG
24W S OF 18N...WITH N WINDS OF 5 TO 10 KT WITHIN 60 NM N OF THE
SURFACE TROUGH AND W TO NW WINDS OF 10 TO 15 KT WITHIN 60 NM S
OF THE SURFACE TROUGH. LOW LEVEL CONVERGENCE IS SUPPORTING
SCATTERED SHOWERS WITHIN 60 NM EITHER SIDE OF THE SURFACE TROUGH.

$$
COHEN




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