[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 011055
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SAT NOV 01 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0945 UTC.

...THE ITCZ...
ITCZ AXIS IS ANALYZED ALONG 10N12W 9N20W 12N35W 10N52W 10N63W.
TWO SURFACE TROUGHS REMAIN EMBEDDED WITHIN THE ITCZ. ONE TROUGH
EXTENDS FROM SW OF THE CANARY ISLANDS NEAR 15N27W TO 11N28W TO
7N29W.  THIS TROUGH COINCIDES WITH BOTH A WESTWARD-MOVING SURGE
IN DEEP LAYER MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT
FROM CIMSS...AND A MAXIMUM IN LOW LEVEL CYCLONIC CIRCULATION
BASED ON CIMSS WAVETRAK PRODUCT. SCATTERED MODERATE CONVECTION
IS WITHIN 210 NM EITHER SIDE OF THE TROUGH N OF 12N...WHICH IS
BEING ENHANCED BY UPPER LEVEL DIVERGENCE. THE SECOND TROUGH
EXTENDS FROM 17N47W TO 14N48W TO 10N48W AND COINCIDES WITH
ANOTHER WESTWARD-MOVING SURGE IN DEEP LAYER MOISTURE. MOST OF
THE CONVECTION ASSOCIATED WITH THIS TROUGH IS CURRENTLY TO ITS
EAST...WITH SCATTERED MODERATE CONVECTION FROM 12N-17N BETWEEN
31W-46W. THIS CONVECTION IS BEING ENHANCED BY UPPER LEVEL
DIVERGENCE IN THE PRESENCE OF DEEP MOISTURE. ELSEWHERE...
SCATTERED MODERATE CONVECTION IS OCCURRING WITHIN 60 NM N AND S
OF ITCZ AXIS BETWEEN 14W-24W. ADDITIONALLY...AN EAST-TO-WEST
SURFACE TROUGH IS S OF THE ITCZ AXIS W OF THE W COAST OF
AFRICA...AND EXTENDS FROM 6N12W TO 4N18W TO 5N25W. LOW LEVEL
CONVERGENCE NEAR THIS TROUGH IS SUPPORTING SCATTERED MODERATE
CONVECTION WITHIN 150 NM N AND S OF THIS FEATURE.

...DISCUSSION...

GULF OF MEXICO...
A SURFACE RIDGE OF HIGH PRESSURE IS AFFECTING MUCH OF THE GULF
REGION. THIS SURFACE RIDGE IS ANCHORED BY A 1031 MB SURFACE HIGH
OVER THE SE CONUS. SUBSIDENCE IN THE VICINITY OF THE RIDGE IS
RESULTING IN FAIR WEATHER CONDITIONS ACROSS MUCH OF THE GULF
REGION. ALOFT...UPPER LEVEL MOISTURE IS EMBEDDED WITHIN THE BASE
OF AN UPPER LEVEL TROUGH THAT COVERS MUCH OF THE GULF...AND IS
RESULTING IN HIGH CLOUDINESS OVER THE SE GULF. ACROSS THE N AND
W GULF...DEEP LAYER DRY AIR AND STRONG MID/UPPER-LEVEL WESTERLY
AND NORTHWESTERLY FLOW ARE PRESENT. THE UPPER LEVEL PATTERN IS
FORECAST TO CHANGE OVER THE NEXT DAY AS A CLOSED UPPER LEVEL LOW
AND ASSOCIATED UPPER TROUGH AND UPPER MOISTURE...CURRENTLY
CENTERED OVER N MISSISSIPPI...APPROACH THE N GULF. HOWEVER...
COMPUTER MODEL GUIDANCE INDICATES THAT THESE FEATURES COULD
TEMPORARILY WEAKEN AS THEY BECOME OVERTAKEN BY AN
EASTWARD-MOVING UPPER RIDGE CURRENTLY OVER THE PLAINS OF THE
CONUS. ADDITIONALLY...STRONG N TO NE SURFACE WINDS ARE BLOWING
THROUGH THE ISTHMUS OF TEHUANTEPEC RESULTING IN GALE FORCE WINDS
IN THE E PACIFIC REGION.

CARIBBEAN SEA...
ANTICYCLONIC FLOW AROUND AN UPPER HIGH CENTERED NEAR 15N72W
COVERS MUCH OF THE CARIBBEAN...WITH DEEP MOISTURE OVER THE W
CARIBBEAN. UPPER LEVEL DIVERGENCE SW OF THE UPPER HIGH IS
SUPPORTING SCATTERED MODERATE/ISOLATED STRONG CONVECTION OVER
THE W CARIBBEAN FROM 9N-18N BETWEEN 76W-84W...AFFECTING PORTIONS
OF PANAMA...COSTA RICA...AND N COLOMBIA...WHERE LOW LEVEL
CONVERGENCE NEAR THE E PACIFIC ITCZ IS ENHANCING THE CONVECTION.
ADDITIONALLY...A SURFACE TROUGH EXTENDS FROM E CUBA NEAR 20N75W
TO 18N79W TO NE NICARAGUA NEAR 15N84W. A RECENT ASCAT PASS
DEPICTS NE WINDS OF 15 TO 20 KT NW OF THE SURFACE TROUGH...AND
NE TO E WINDS OF 10 TO 15 KT SE OF THE SURFACE TROUGH. THE
CORRESPONDING LOW LEVEL CONVERGENCE NEAR THIS TROUGH...COMBINED
WITH DEEP MOISTURE...IS SUPPORTING ISOLATED MODERATE CONVECTION
WITHIN 60 NM EITHER SIDE OF THE SURFACE TROUGH. DEEP LAYER DRY
AIR E OF THE UPPER HIGH IS RESULTING IN MAINLY FAIR WEATHER
ACROSS THE E CARIBBEAN.

ATLANTIC OCEAN...
DEEP LAYER DRY AIR IS EMBEDDED WITHIN A BROAD UPPER LEVEL TROUGH
OVER THE W ATLC...WHERE GENERALLY FAIR WEATHER IS PRESENT. AT
THE SAME TIME...A SURFACE RIDGE OF HIGH PRESSURE...ANCHORED BY A
1031 MB SURFACE HIGH OVER THE SE CONUS...IS RESULTING IN
SUBSIDENCE ACROSS MUCH OF THE W ATLC. FARTHER TO THE E...A
SURFACE STATIONARY FRONT EXTENDS FROM 32N53W TO 29N57W TO
25N63W...AND A SURFACE TROUGH EXTENDS FROM 25N63W TO 22N70W TO E
CUBA NEAR 20N75W. ATMOSPHERIC LIFT IN MOIST SOUTHWESTERLY FLOW
ALOFT IS SUPPORTING SCATTERED SHOWERS WITHIN 60 NM EITHER SIDE
OF THE SURFACE STATIONARY FRONT AND SURFACE TROUGH...WHICH ARE
BEING SUPPORTED BY UPPER DIFFLUENCE NEAR AN UPPER RIDGE FROM
22N-30N BETWEEN 48W-58W. FARTHER TO THE E...A COMPACT UPPER
LEVEL TROUGH IS PRESENT WITH AN AXIS THAT EXTENDS FROM 27N48W TO
16N49W TO 10N48W. ALSO...A DEEP LAYER TROUGH IS N OF 21N E OF
41W...WHICH IS SUPPORTING A SURFACE COLD FRONT EXTENDING FROM
32N9W TO 28N18W TO 32N30W THAT IS MOVING SOUTHWARD ACROSS THE
CANARY ISLANDS. ISOLATED SHOWERS ARE OCCURRING WITHIN 60 NM
EITHER SIDE OF THE COLD FRONT E OF 16W. OVER THE TROPICAL
ATLC...AN EAST-TO-WEST UPPER RIDGE IS ALONG 11N BETWEEN THE
AFRICAN COAST AND 43W. UPPER LEVEL DIVERGENCE NEAR THIS RIDGE IS
ENHANCING THE CONVECTION ASSOCIATED WITH THE SURFACE TROUGHS
THAT ARE EMBEDDED WITHIN THE ITCZ.

OF NOTE...NOVEMBER IS THE LAST MONTH OF THE ATLANTIC HURRICANE
SEASON. SO FAR...FIFTEEN NAMED STORMS HAVE DEVELOPED...OF WHICH
SEVEN BECAME HURRICANES...WITH FOUR OF THE HURRICANES ATTAINING
MAJOR HURRICANE STATUS. IN ADDITION...A SHORT-LIVED TROPICAL
DEPRESSION FORMED IN OCTOBER. THE MOST POWERFUL HURRICANES SEEN
THIS SEASON ARE GUSTAV AND IKE...BOTH CAT 4 ON THE SAFFIR
SIMPSON SCALE.

$$
COHEN/GR

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