[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 211153
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST SUN DEC 21 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
1115 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 6N9W 5N21W 6N34W 7N45W 3N55W. A SURFACE
TROUGH IS EMBEDDED WITHIN THE ITCZ. THIS SURFACE TROUGH EXTENDS
FROM 12N35W TO 8N36W TO 3N37W...WITH LOW LEVEL CONVERGENCE
SUPPORTING SCATTERED MODERATE/ISOLATED STRONG CONVECTION FROM
10N-14N BETWEEN 32W-35W. ELSEWHERE...SCATTERED MODERATE
CONVECTION IS S OF 4N BETWEEN 8W-15W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 1N-7N BETWEEN
17W-30W.

...DISCUSSION...

GULF OF MEXICO...
A 1019 MB SURFACE HIGH IS OVER THE W FLORIDA PENINSULA NEAR
27N82W...AND A 1018 MB SURFACE HIGH IS OVER THE W ATLC NEAR
28N69W. BROAD SURFACE ANTICYCLONIC FLOW AROUND THESE SURFACE
HIGHS COVERS MUCH OF THE GULF REGION. ALSO...SUBSIDENCE
ASSOCIATED WITH THESE SURFACE HIGHS IS RESULTING IN ATMOSPHERIC
STABILITY AND FAIR WEATHER CONDITIONS ACROSS MUCH OF THE GULF
REGION. THIS STABILITY IS BEING ENHANCED AROUND A BROAD UPPER
LEVEL RIDGE...WHICH EXTENDS INTO THE W GULF. THE AXIS OF THIS
UPPER RIDGE EXTENDS FROM THE SW CARIBBEAN INTO THE W ATLC. THIS
UPPER RIDGE IS ASSOCIATED WITH RELATIVELY LIGHT AND BROAD
ANTICYCLONIC FLOW ALOFT...AND DEEP LAYER DRY AIR...AFFECTING
MUCH OF THE GULF REGION. FARTHER TO THE N...A DEEP LONGWAVE
TROUGH WITH AN ASSOCIATED STRONG UPPER LEVEL JET MAXIMUM OVER
THE CENTRAL CONUS IS SUPPORTING A SURFACE FRONT EXTENDING FROM
EASTERN NORTH CAROLINA TO SE TEXAS AND NORTHWESTWARD ACROSS THE
CENTRAL ROCKY MOUNTAINS OF THE CONUS. A SURFACE TROUGH IS S OF
THE COLD FRONT...AND THIS SURFACE TROUGH EXTENDS FROM THE SE
TEXAS COAST NEAR 29N96W TO 27N99W TO N MEXICO NEAR 26N100W AND
EXTENDS FARTHER SOUTHWARD INTO CENTRAL MEXICO. THIS FRONT IS
EXPECTED TO BEGIN MOVING SOUTHWARD ACROSS THE GULF TODAY AS A
COLD FRONT. NATIONAL WEATHER SERVICE DOPPLER RADARS ACROSS SE
TEXAS AND S LOUISIANA INDICATE THAT SCATTERED SHOWERS ARE
OCCURRING OVER THE NW GULF N OF 28N BETWEEN 92W-96W IN RESPONSE
TO LOW LEVEL CONVERGENCE ASSOCIATED WITH THE SURFACE TROUGH AND
SURFACE COLD FRONT. INCREASED N TO NE SURFACE WINDS ARE FORECAST
IN THE WAKE OF THE COLD FRONT...WITH GALE FORCE WINDS FORECAST N
OF THE FRONT ACROSS PORTIONS OF THE NW GULF. RELATIVELY COOLER
AND DRIER CONDITIONS ARE PRESENT IN THE WAKE OF THE COLD FRONT.

CARIBBEAN SEA...
AN UPPER RIDGE COVERS MUCH OF THE W AND CENTRAL CARIBBEAN...WITH
THE AXIS OF THIS UPPER RIDGE EXTENDING FROM N COLOMBIA NEAR
11N73W TO 17N75W TO HAITI NEAR 20N72W TO THE W ATLC. SUBSIDENCE
AND ATMOSPHERIC STABILITY ASSOCIATED WITH THIS UPPER RIDGE COVER
THE CARIBBEAN REGION...WHERE GENERALLY DEEP LAYER DRY AIR IS
PRESENT. THESE FACTORS ARE RESULTING IN FAIR WEATHER CONDITIONS
ACROSS MUCH OF THE CARIBBEAN REGION. THE SOUTHERN PERIPHERY OF
THE BROAD SURFACE ANTICYCLONIC FLOW AROUND THE AFOREMENTIONED
SURFACE HIGHS OVER THE W FLORIDA PENINSULA AND W ATLC IS
BRINGING NE TO E SURFACE WINDS OF 10 TO 15 KT TO THE CARIBBEAN
REGION. UPPER LEVEL MOISTURE IS STREAMING NORTHWARD FROM SOUTH
AMERICA INTO THE SE CARIBBEAN...WITH ISOLATED SHOWERS ACROSS THE
SE CARIBBEAN S OF 12N E OF 65W.

ATLANTIC OCEAN...
A 1018 MB SURFACE HIGH IS CENTERED IN THE W ATLC NEAR 28N69W...
WITH A 1019 MB SURFACE HIGH OVER THE W FLORIDA PENINSULA NEAR
27N82W. THESE SURFACE HIGHS ARE BRINGING SUBSIDENCE AND FAIR
WEATHER CONDITIONS TO MUCH OF THE W ATLC. THIS SUBSIDENCE IS
BEING ENHANCED AROUND AN UPPER RIDGE WITH AN AXIS EXTENDING FROM
THE SW CARIBBEAN TO HAITI NEAR 20N72W TO 25N74W TO 30N74W.
DURING THE NEXT DAY...THE FRONT DESCRIBED IN THE GULF OF MEXICO
SECTION ABOVE IS ALSO FORECAST TO BEGIN TO MOVE SOUTHWARD ACROSS
THE W ATLC AS A COLD FRONT...WITH RELATIVELY COOLER AND DRIER
CONDITIONS IN THE WAKE OF THE COLD FRONT. FARTHER TO THE
E...SATELLITE IMAGERY AND COMPUTER MODEL GUIDANCE DEPICT TWO
SEPARATE SURFACE TROUGHS OVER THE CENTRAL ATLC. ONE OF THESE
SURFACE TROUGHS EXTENDS FROM 25N47W TO A 1011 MB SURFACE LOW
NEAR 21N49W TO 16N50W...AND THE OTHER SURFACE TROUGH EXTENDS
FROM 26N43W TO 21N45W TO 16N46W. LOW LEVEL CONVERGENCE
ASSOCIATED WITH THIS SURFACE LOW AND SURFACE TROUGHS IS
RESULTING IN ISOLATED SHOWERS FROM 18N-25N BETWEEN 43W-51W. THIS
SHOWER ACTIVITY IS BEING ENHANCED BY ATMOSPHERIC INSTABILITY IN
THE VICINITY OF AN UPPER TROUGH WITH AN AXIS EXTENDING FROM
15N56W TO 23N43W TO 32N37W TO N OF THE DISCUSSION AREA.
ALSO...UPPER LEVEL DIVERGENCE ASSOCIATED WITH A 70-80-KT UPPER
LEVEL JET MAXIMUM E OF THE UPPER TROUGH AXIS IS SUPPORTING
NUMEROUS SHOWERS FROM 22N-31N BETWEEN 31W-40W. ACROSS THE E
ATLC...SUBSIDENCE ASSOCIATED WITH A SURFACE RIDGE OVER THE E
ATLC IS INHIBITING DEEP CONVECTION N OF 19N E OF 28W. HOWEVER...
ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER LOW NEAR 33N18W
IS RESULTING IN SCATTERED SHOWERS N OF 30N BETWEEN 15W-23W.
ALSO...LOW LEVEL CONVERGENCE IS SUPPORTING ISOLATED SHOWERS
WITHIN 60 NM EITHER SIDE OF A SURFACE TROUGH EXTENDING FROM
31N11W TO 32N11W TO NE OF THE DISCUSSION AREA. FARTHER TO THE
S...A SURFACE TROUGH EXTENDS FROM 13N49W TO 10N51W TO 7N52W. LOW
LEVEL CONVERGENCE IN THE VICINITY OF THIS SURFACE TROUGH IS
RESULTING IN SCATTERED SHOWERS FROM 7N-11N BETWEEN
50W-56W...WHICH ARE BEING ENHANCED BY UPPER LEVEL DIVERGENCE.
ALSO...A SURFACE TROUGH...EXTENDING FROM 12N35W TO 8N36W TO
3N37W...IS EMBEDDED WITHIN THE ITCZ...WITH LOW LEVEL CONVERGENCE
ASSOCIATED WITH THIS SURFACE TROUGH SUPPORTING SCATTERED
MODERATE/ISOLATED STRONG CONVECTION FROM 10N-14N BETWEEN
32W-35W. AN UPPER RIDGE IS S OF 16N BETWEEN THE AFRICAN COAST
AND 36W. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH THIS UPPER RIDGE
IS ENHANCING THE CONVECTION ASSOCIATED WITH THE ITCZ E OF 36W.

$$
COHEN


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