[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 201129
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST SAT DEC 20 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
1045 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 9N12W 6N24W 6N35W 10N48W 6N59W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 3N-8N BETWEEN
15W-24W. SCATTERED MODERATE CONVECTION IS FROM 2N-10N BETWEEN
28W-37W. SCATTERED MODERATE CONVECTION IS ALSO WITHIN 120 NM
EITHER SIDE OF THE ITCZ AXIS BETWEEN 42W-50W. SCATTERED MODERATE
CONVECTION IS ALSO WITHIN 120 NM EITHER SIDE OF THE ITCZ AXIS
BETWEEN 55W-58W.

...DISCUSSION...

GULF OF MEXICO...
A 1021 MB SURFACE HIGH IS OVER THE E GULF NEAR 28N83W...AND A
1021 MB SURFACE HIGH IS OVER THE W ATLC NEAR 28N74W. 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 IN THE VICINITY OF A BROAD UPPER
LEVEL RIDGE EXTENDING ACROSS THE GULF REGION FROM AN UPPER HIGH
CENTERED NW OF HISPANIOLA NEAR 21N73W. 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 THE MID-ATLANTIC
STATES ACROSS THE SOUTHERN PLAINS AND INTO THE SOUTHERN ROCKY
MOUNTAIN REGION OF THE CONUS. THE FRONT IS EXPECTED TO MOVE
SOUTHWARD ACROSS THE GULF ON SUNDAY AND MONDAY AS A COLD FRONT.
INCREASED NE SURFACE WINDS ARE FORECAST IN THE WAKE OF THE COLD
FRONT...WITH GALE FORCE WINDS EXPECTED SUNDAY AFTERNOON AND
NIGHT FOR PORTIONS OF THE NW GULF.

CARIBBEAN SEA...
SUBSIDENCE IN WESTERLY FLOW ALOFT AND ATMOSPHERIC STABILITY
COVER THE CARIBBEAN REGION...WHERE GENERALLY DEEP LAYER DRY AIR
IS PRESENT. THESE FACTORS ARE RESULTING IN FAIR WEATHER
CONDITIONS ACROSS MUCH THE CARIBBEAN REGION. THE SOUTHERN
PERIPHERY OF THE BROAD SURFACE ANTICYCLONIC FLOW AROUND THE
AFOREMENTIONED SURFACE HIGHS OVER THE E GULF AND W ATLC IS
BRINGING NE SURFACE WINDS OF 10 TO 20 KT TO THE CARIBBEAN
REGION...EXCEPT UP TO 25 KT NEAR THE COAST OF COLOMBIA. UPPER
LEVEL MOISTURE IS STREAMING NORTHWARD FROM SOUTH AMERICA INTO
THE SE CARIBBEAN...WITH ISOLATED SHOWERS ACROSS THE S CARIBBEAN
S OF 12N E OF 68W. ALSO...A SURFACE TROUGH EXTENDS FROM THE W
ATLC NEAR 27N58W TO 22N63W TO THE NE CARIBBEAN NEAR
17N66W...WITH SATELLITE IMAGERY DEPICTING CYCLONIC MOTION OF
CLOUDS IN THE VICINITY OF THIS SURFACE TROUGH. LOW LEVEL
CONVERGENCE IS RESULTING IN ISOLATED SHOWERS WITHIN 60 NM EITHER
SIDE OF THIS SURFACE TROUGH.

ATLANTIC OCEAN...
A 1021 MB SURFACE HIGH IS CENTERED IN THE W ATLC NEAR 28N74W...
WITH A 1021 MB SURFACE HIGH IN THE E GULF OF MEXICO NEAR 28N83W.
THESE SURFACE HIGHS ARE BRINGING SUBSIDENCE AND FAIR WEATHER
CONDITIONS TO MUCH OF THE W ATLC. THIS SUBSIDENCE IS BEING
ENHANCED IN THE VICINITY OF THE UPPER HIGH NW OF HISPANIOLA NEAR
21N73W. NORTHERLY UPPER LEVEL FLOW TO THE E OF THIS UPPER HIGH
IS ADVECTING UPPER LEVEL MOISTURE ACROSS PORTIONS OF THE W ATLC.
FARTHER TO THE E...A SURFACE TROUGH OVER THE CENTRAL ATLC
EXTENDS FROM 29N46W TO 26N48W TO 22N48W. LOW LEVEL CONVERGENCE
ASSOCIATED WITH THIS SURFACE TROUGH IS RESULTING IN NUMEROUS
SHOWERS FROM 21N-30N BETWEEN 39W-44W. THIS ACTIVITY IS BEING
ENHANCED BY ATMOSPHERIC INSTABILITY IN THE VICINITY OF AN UPPER
TROUGH WITH AN AXIS EXTENDING FROM 18N60W TO 27N48W TO 32N45W TO
N OF THE DISCUSSION AREA. ALSO...UPPER LEVEL DIVERGENCE
ASSOCIATED WITH AN 80-90-KT UPPER LEVEL JET MAXIMUM E OF THE
UPPER TROUGH AXIS IS SUPPORTING THIS ACTIVITY...ALONG WITH LOW
LEVEL CONVERGENCE ASSOCIATED WITH A WEAKENING SURFACE STATIONARY
FRONT EXTENDING FROM NW OF THE DISCUSSION AREA TO 32N58W TO
31N56W AND A SURFACE COLD FRONT EXTENDING FROM 32N45W TO NE OF
THE DISCUSSION AREA. ACROSS THE E ATLC...SUBSIDENCE ASSOCIATED
WITH A SURFACE RIDGE EXTENDING SOUTHWESTWARD FROM A 1036 MB
SURFACE HIGH NEAR 45N10W IS GENERALLY INHIBITING DEEP CONVECTION
N OF 16N E OF 35W. HOWEVER...ATMOSPHERIC INSTABILITY ASSOCIATED
WITH AN UPPER LOW NEAR 31N18W IS RESULTING IN SCATTERED SHOWERS
N OF 28N BETWEEN 16W-22W. THIS ACTIVITY IS BEING ENHANCED BY LOW
LEVEL CONVERGENCE IN THE VICINITY OF A SURFACE TROUGH EXTENDING
FROM 31N11W TO 32N10W TO NE OF THE DISCUSSION AREA. FARTHER TO
THE S...A SURFACE TROUGH EXTENDS FROM 27N58W TO 22N63W TO THE NE
CARIBBEAN NEAR 17N66W...WITH SATELLITE IMAGERY DEPICTING
CYCLONIC MOTION OF CLOUDS IN THE VICINITY OF THIS SURFACE
TROUGH. LOW LEVEL CONVERGENCE IS RESULTING IN ISOLATED SHOWERS
WITHIN 60 NM EITHER SIDE OF THIS SURFACE TROUGH. ALSO...AN UPPER
RIDGE IS S OF 14N BETWEEN 19W-51W. UPPER LEVEL DIFFLUENCE
ASSOCIATED WITH THIS UPPER RIDGE IS ENHANCING THE CONVECTION
ASSOCIATED WITH THE ITCZ.

$$
COHEN




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