[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 040005
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI OCT 03 2008

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
2315 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 18W/19W S OF 17N MOVING W NEAR 10 KT.
COMPUTER MODEL GUIDANCE SHOWS ENHANCED LOW LEVEL CIRCULATION
COINCIDING WITH THE WAVE AXIS...WHERE DEEP LAYER MOISTURE IS
MAXIMIZED BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS.
ISOLATED MODERATE CONVECTION IS WITHIN 120 NM EITHER SIDE OF THE
WAVE AXIS.

TROPICAL WAVE IS ALONG 47W/48W S OF 17N MOVING W NEAR 10 KT.
WAVE IS EMBEDDED WITHIN AN AREA OF ENHANCED DEEP LAYER MOISTURE.
COMPUTER MODEL GUIDANCE DEPICTS LOW LEVEL CIRCULATION ALONG WAVE
AXIS. ISOLATED SHOWERS ARE OCCURRING WITHIN 150 NM W OF THE WAVE
AXIS N OF 12N.

TROPICAL WAVE IS ALONG 58W/59W S OF 17N MOVING W 10-15 KT. THIS
WAVE COINCIDES WITH A MAXIMUM IN CIMSS WAVETRACK DERIVED LOW
LEVEL CIRCULATION...AS WELL AS A MAXIMUM IN TOTAL PRECIPITABLE
WATER. SCATTERED MODERATE CONVECTION IS WITHIN 120 NM EITHER
SIDE OF THE WAVE AXIS N OF 13N...WITH ISOLATED MODERATE
CONVECTION WITHIN 90 NM EITHER SIDE OF THE WAVE AXIS S OF 10N.

...THE ITCZ...
THE ITCZ AXIS IS ANALYZED ALONG 13N16W 9N25W 8N40W 11N52W
10N63W. ISOLATED MODERATE CONVECTION IS OVER W AFRICA FROM
11N-16N BETWEEN 15W-18W...INCLUDING GUINEA-BISSAU...GAMBIA...AND
SENEGAL. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS
WITHIN 150 NM N OF THE AXIS AND 210 NM S OF THE AXIS FROM THE W
AFRICAN COAST TO 31W. SCATTERED MODERATE CONVECTION IS WITHIN
180 NM S OF THE ITCZ AXIS FROM 61W WESTWARD TO THE SOUTH
AMERICAN COAST...IMPACTING NE VENEZUELA AND N GUYANA.

...DISCUSSION...

GULF OF MEXICO...
DRY AND STABLE AIR IN THE BASE OF A BROAD UPPER TROUGH IS OVER
THE GULF REGION AND E CONUS...WITH STRONG WESTERLY FLOW ALOFT
OVER THE N GULF. SUBSIDENCE RESULTING FROM A WEAK SURFACE RIDGE
OVER THE N GULF IS ALSO HELPING TO RESULT IN FAIR WEATHER ACROSS
MUCH OF THE GULF. A STATIONARY FRONT EXTENDS FROM JUST NW OF
CUBA NEAR 22N84W NE TO 24N80W TO THE SW ATLC. SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS ARE OCCURRING WITHIN 90 NM EITHER
SIDE OF THE FRONT...WHERE GREATER ATMOSPHERIC LIFT AND DEEP
MOISTURE PERSISTS.

CARIBBEAN SEA...
OVER THE W CARIBBEAN...A WEAK UPPER HIGH IS NEAR 17N82W...WITH
MOIST DIFFLUENT UPPER FLOW TO THE E OF THIS HIGH. ALSO OVER THE
W CARIBBEAN...A SURFACE TROUGH EXTENDS FROM W NICARAGUA NEAR
12N87W TO A 1011 MB SURFACE LOW IN THE GULF OF HONDURAS NEAR
17N86W TO 20N85W. SATELLITE IMAGERY DEPICTS A BROAD LOW LEVEL
CIRCULATION IN THE VICINITY OF THE SURFACE LOW AND TROUGH.
SURFACE CONVERGENCE AND UPPER DIFFLUENCE NEAR THESE FEATURES ARE
RESULTING IN SCATTERED MODERATE/ISOLATED STRONG CONVECTION OVER
THE W CARIBBEAN W OF 77W...INCLUDING JAMAICA...CUBA...
HONDURAS...AND NICARAGUA. A WEAK UPPER RIDGE IS OVER THE CENTRAL
CARIBBEAN...WHERE MAINLY FAIR WEATHER IS PRESENT. OVER THE E
CARIBBEAN...AN UPPER LOW IS CENTERED JUST W OF THE LEEWARD
ISLANDS NEAR 16N63W...WITH A WEAK UPPER TROUGH EXTENDING TO THE
SW OF THE LOW TO NW VENEZUELA. MOIST SOUTHERLY FLOW ALOFT
COMBINED WITH THE TROPICAL WAVE ALONG 58W/59W IS RESULTING IN
ISOLATED SHOWERS OVER THE E CARIBBEAN E OF 63W AND N OF
15N...WHICH ARE IMPACTING THE LEEWARD ISLANDS.

ATLANTIC OCEAN...
STRONG SOUTHWESTERLY FLOW ALOFT E OF A DEEP TROUGH OVER THE E
CONUS IS IMPACTING PORTIONS OF THE SW ATLC. A COLD FRONT EXTENDS
FROM A 1013 MB SURFACE LOW NEAR 32N73W SW TO NEAR 27N77W. THIS
FRONT EXTENDS FURTHER TO THE SW AS A STATIONARY FRONT TO 24N80W
TO 23N84W. DRY AND STABLE AIR IN THE BASE OF THE UPPER TROUGH
CONTINUES TO AFFECT THE SW ATLC TO THE NW OF THE SURFACE
FRONT...WITH LINGERING MOISTURE AND ATMOSPHERIC LIFT ALONG AND
SE OF THE FRONT. AS A RESULT...SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS ARE WITHIN 180 NM SE OF THE SURFACE FRONT...
AFFECTING CUBA AND THE BAHAMAS. TO THE E...AN UPPER HIGH IS
CENTERED NEAR 32N57W...WITH ITS ASSOCIATED UPPER RIDGE EXTENDING
FROM THE HIGH INTO THE CENTRAL CARIBBEAN. THIS HIGH AND RIDGE
ARE RESULTING IN DRY AND STABLE ATMOSPHERIC CONDITIONS OVER MUCH
OF THE CENTRAL ATLC. FARTHER TO THE E...A COMPACT AND DEEP LOW
IS CENTERED NEAR 22N46W WITH AN UPPER TROUGH EXTENDING NE OF THE
THE LOW TO NEAR 29N37W. THESE FEATURES ARE SUPPORTING A SURFACE
TROUGH THAT EXTENDS FROM 32N44W S TO 28N44W TO 24N44W. DEEP
LAYER DRY AIR OVER THE SURFACE TROUGH IS INHIBITING CONVECTION
NEAR MUCH OF THE SURFACE TROUGH. HOWEVER...TO THE S OF THIS
SURFACE TROUGH...SAHARAN AIR LAYER CONTINUES TRACKING TO THE W
INTO A MOIST AIRMASS. LOW LEVEL CONVERGENCE AT THE BOUNDARY IS
SUPPORTING SCATTERED MODERATE/ISOLATED STRONG CONVECTION WITHIN
150 NM OF A LINE FROM 20N44W S TO 15N38W TO 10N36W...WHICH IS
BEING ENHANCED BY LIFT IN SW FLOW ALOFT. FARTHER TO THE E...A
BROAD UPPER TROUGH IS N OF 23N BETWEEN THE W AFRICAN COAST AND
35W...WITH DRY AIR EMBEDDED WITHIN THIS TROUGH. OVER THE
TROPICAL ATLC...A BROAD E/W UPPER RIDGE EXTENDS FROM W AFRICA
ALONG 12N TO 52W AND DOMINATES THE THE TROPICAL ATLC.

$$
COHEN



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