[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 011747
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT WED JUL 01 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 NEW TROPICAL WAVE HAS MOVED OFF THE W AFRICAN COAST AND IS
APPROXIMATELY ALONG 20W S OF 13N. RECENT VISIBLE SATELLITE
IMAGERY IN THIS AREA SHOWS THIS WELL-DEFINED FEATURE MOVING W
NEAR 15 KT IN THE WAKE OF A LARGE MESOSCALE CONVECTIVE SYSTEM
THAT RECENTLY MOVED OFF THE W AFRICAN COAST. ALSO...CYCLONIC
MOTION OF LOW LEVEL CLOUDS IS EVIDENT NEAR THIS FEATURE.
TIME-HEIGHT ANALYSES FROM DAKAR SENEGAL INDICATE AN ABRUPT SHIFT
OF ANOMALOUS FLOW BELOW THE 600 MB LEVEL FROM NORTHEASTERLY TO
SOUTHEASTERLY AROUND 01/0900 UTC...INDICATING THAT WAVE PASSAGE
LIKELY OCCURRED AT DAKAR AROUND THAT TIME. THIS FEATURE
COINCIDES WITH A DISTINCT MAXIMUM IN DEEP LAYER MOISTURE BASED
ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. THUS...A
TROPICAL WAVE WILL BE ADDED TO THE 01/1800 UTC SURFACE ANALYSIS
OVER THE TROPICAL E ATLC. CONSIDERABLE LOW/MID-LEVEL DRY SAHARAN
AIR IS LIMITING THE AREAL COVERAGE OF DEEP CONVECTION NEAR THIS
WAVE...HOWEVER SCATTERED MODERATE CONVECTION IS FROM 6N-10N
BETWEEN 13W-22W.

A TROPICAL WAVE IS ALONG 34W S OF 14N MOVING W 15-20 KT. THIS
WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON
THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. RECENT VISIBLE
SATELLITE IMAGERY INDICATES THAT THE WAVE COINCIDES WITH AN
INVERTED-V PATTERN IN THE COVERAGE OF LOW LEVEL CLOUDS.
SATELLITE-DERIVED WINDS INDICATE CYCLONIC CURVATURE IN THE LOW
LEVEL FLOW NEAR THIS WAVE. SCATTERED MODERATE CONVECTION IS FROM
7N-9N BETWEEN 34W-37W.

A TROPICAL WAVE EXTENDS ACROSS THE FAR E CARIBBEAN FROM 15N60W
TO THE COAST OF VENEZUELA NEAR 10N63W TO 2N65W MOVING W 15-20
KT. THIS WAVE HAS BEEN ADJUSTED WESTWARD BASED ON RECENT SURFACE
OBSERVATIONS...SCATTEROMETER DATA...AND TOTAL PRECIPITABLE WATER
DATA. IN PARTICULAR...SURFACE OBSERVATIONS ACROSS THE WINDWARD
ISLANDS...ALONG WITH THE QUIKSCAT PASS AROUND 01/0945 UTC...
INDICATE CYCLONIC CURVATURE IN THE LOW LEVEL FLOW ACROSS THE
WAVE. SURFACE PRESSURE RISES HAVE RECENTLY BEEN NOTED ACROSS THE
WINDWARD ISLANDS FOLLOWING WAVE PASSAGE. ADDITIONALLY...RECENT
VISIBLE SATELLITE IMAGERY INDICATES THAT THE WAVE CORRESPONDS
WITH AN INVERTED-V PATTERN IN THE COVERAGE OF LOW LEVEL CLOUDS.
THIS WAVE ALSO COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE
BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS.
SCATTERED MODERATE CONVECTION IS FROM 12N-14N BETWEEN 62W-65W.

A TROPICAL WAVE IS ALONG 97W/98W S OF 17N MOVING W NEAR 15 KT.
THIS WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED
ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. WHILE THIS
WAVE IS PRIMARILY IN THE E PACIFIC REGION...IT IS SUPPORTING
SCATTERED MODERATE CONVECTION FROM 16N-19N BETWEEN 92W-97W
INCLUDING PORTIONS OF S MEXICO AND THE ADJACENT WATERS OF THE SW
GULF OF MEXICO.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 11N15W 7N23W 7N36W 5N48W 6N59W.
SCATTERED MODERATE CONVECTION IS FROM 5N-8N BETWEEN 23W-27W.
SCATTERED MODERATE CONVECTION IS ALSO FROM 3N-6N BETWEEN 38W-44W
AND FROM 6N-9N BETWEEN 51W-59W.

...DISCUSSION...

GULF OF MEXICO...
A DEEP LAYER TROUGH OVER THE E UNITED STATES EXTENDS INTO THE NE
GULF. ATMOSPHERIC LIFT IN MOIST SOUTHWESTERLY FLOW ALOFT E OF
THE TROUGH AXIS IS SUPPORTING SCATTERED SHOWERS AND
THUNDERSTORMS N OF 25N E OF 90W INCLUDING PORTIONS OF THE W
FLORIDA PENINSULA. THIS ACTIVITY IS BEING ENHANCED BY ABUNDANT
DEEP LAYER MOISTURE OVER THE NE GULF AND FLORIDA PENINSULA.
ALSO...AN UPPER LEVEL HIGH OVER THE SW GULF IS CENTERED NEAR
22N96W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH THIS HIGH IS
SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS S OF 24N
W OF 95W. THIS ACTIVITY IS ALSO BEING SUPPORTED BY LOW LEVEL
CONVERGENCE NEAR THE TROPICAL WAVE ALONG 97W/98W S OF 17N
DISCUSSED IN THE TROPICAL WAVES SECTION ABOVE. ACROSS THE S
CENTRAL AND SE GULF...DEEP LAYER DRY AIR IS SUPPORTING GENERALLY
FAIR WEATHER...WHERE SUBSIDENCE IS OCCURRING IN THE VICINITY OF
A SURFACE RIDGE. THE PRESSURE GRADIENT AROUND THIS SURFACE RIDGE
IS RESULTING IN E TO SE WINDS OF 10 TO 15 KT ACROSS PORTIONS OF
THE SW GULF.

CARIBBEAN SEA...
ACROSS THE W CARIBBEAN...AN UPPER LEVEL LOW IS CENTERED NEAR
15N78W WITH ASSOCIATED ATMOSPHERIC INSTABILITY SUPPORTING
SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE SW CARIBBEAN S OF
13N W OF 76W INCLUDING PORTIONS OF COSTA RICA AND PANAMA. ACROSS
THE NW CARIBBEAN...DEEP LAYER DRY AIR AND SUBSIDENCE IN
NORTHEASTERLY FLOW ALOFT W OF THE UPPER LOW IS SUPPORTING
GENERALLY FAIR WEATHER. ACROSS THE E CARIBBEAN...A BROAD UPPER
LEVEL RIDGE IS PRESENT WITH AN UPPER LEVEL HIGH NEAR 13N67W.
ATMOSPHERIC STABILITY ASSOCIATED WITH THIS UPPER LEVEL HIGH IS
RESULTING IN GENERALLY FAIR WEATHER ACROSS THE E CARIBBEAN.
HOWEVER...CONVECTION ASSOCIATED WITH THE TROPICAL WAVE ACROSS
THE FAR E CARIBBEAN IS BEING SUPPORTED BY UPPER LEVEL DIVERGENCE
ASSOCIATED WITH THE UPPER LEVEL HIGH...AND THIS TROPICAL WAVE IS
DISCUSSED IN THE TROPICAL WAVES SECTION ABOVE. THE SURFACE
PRESSURE GRADIENT S OF A SURFACE RIDGE OVER THE CENTRAL AND E
ATLC IS SUPPORTING E TO SE WINDS OF 20 TO 25 KT ACROSS MUCH OF
THE CARIBBEAN...EXCEPT TO 30 KT NEAR THE COAST OF COLOMBIA.

ATLANTIC OCEAN...
ACROSS THE SW NORTH ATLC...ATMOSPHERIC LIFT IN SOUTHWESTERLY
ALOFT IS INTERACTING WITH DEEP LAYER MOISTURE TO SUPPORT
SCATTERED SHOWERS AND THUNDERSTORMS N OF 28N BETWEEN 70W-79W...
AS WELL AS FROM 24N-27N BETWEEN 76W-79W INCLUDING THE NW
BAHAMAS. TO THE E...DEEP LAYER MOISTURE STREAMING AROUND AN
UPPER LEVEL HIGH CENTERED NEAR 27N70W IS SUPPORTING SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS N OF 29N BETWEEN 46W-55W.
FARTHER TO THE E...GENERALLY FAIR WEATHER IS PRESENT ACROSS MUCH
OF THE CENTRAL AND E ATLC...WHERE SUBSIDENCE IS OCCURRING NEAR A
BROAD SURFACE RIDGE. THIS SURFACE RIDGE IS ASSOCIATED WITH A
1025 MB SURFACE HIGH NEAR 28N30W. HOWEVER...AN UPPER LEVEL
TROUGH AXIS EXTENDS FROM AN UPPER LEVEL LOW NEAR 31N37W TO
22N42W. DIFFLUENCE IN MOIST SOUTHWESTERLY FLOW ALOFT E OF THE
TROUGH AXIS IS SUPPORTING SCATTERED SHOWERS N OF 27N BETWEEN
33W-38W. A BROAD AREA OF LOW/MID-LEVEL DRY SAHARAN AIR COVERS
THE E ATLC S OF 25N TO THE ITCZ E OF 55W AND IS LIMITING THE
AREAL COVERAGE OF DEEP CONVECTION IN THIS AREA.

$$
COHEN




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