[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 210526
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0445 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 6N10W 4N21W 7N33W 6N46W 3N54W. A SURFACE
TROUGH IS EMBEDDED WITHIN THE ITCZ AXIS. THIS SURFACE TROUGH
EXTENDS FROM 12N33W TO 8N35W TO 4N36W...WITH LOW LEVEL
CONVERGENCE SUPPORTING SCATTERED MODERATE CONVECTION WITHIN
180 NM EITHER SIDE OF THIS SURFACE TROUGH N OF 8N. ELSEWHERE...
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 1N-7N
BETWEEN 8W-18W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS
ALSO FROM 2N-7N BETWEEN 19W-22W. NUMEROUS MODERATE/ISOLATED
STRONG CONVECTION IS FROM 2N-8N BETWEEN 23W-28W. SCATTERED
MODERATE CONVECTION IS S OF 5N BETWEEN 45W-51W.

...DISCUSSION...

GULF OF MEXICO...
A 1019 MB SURFACE HIGH IS OVER THE E GULF NEAR 27N83W...AND A
1020 MB SURFACE HIGH IS OVER THE W ATLC NEAR 28N72W. 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 CENTRAL TEXAS AND NORTHWESTWARD ACROSS THE NORTHERN
ROCKY MOUNTAINS OF THE CONUS. THIS 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 FORECAST N OF THE FRONT ACROSS
PORTIONS OF THE NW GULF.

CARIBBEAN SEA...
AN UPPER RIDGE COVERS MUCH OF THE W AND CENTRAL CARIBBEAN...WITH
THE AXIS OF THE UPPER RIDGE EXTENDING FROM N COLOMBIA NEAR
11N73W TO 18N78W TO E CUBA NEAR 21N76W 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 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 TO E
SURFACE WINDS OF 10 TO 20 KT TO THE CARIBBEAN REGION...EXCEPT UP
TO 25 KT NEAR THE COAST BETWEEN 75W-80W AND NEAR THE COAST OF
COLOMBIA. UPPER LEVEL MOISTURE IS STREAMING NORTHWARD FROM SOUTH
AMERICA INTO THE SE CARIBBEAN...WITH ISOLATED SHOWERS ACROSS THE
SE CARIBBEAN S OF 13N E OF 66W.

ATLANTIC OCEAN...
A 1020 MB SURFACE HIGH IS CENTERED IN THE W ATLC NEAR 28N72W...
WITH A 1019 MB SURFACE HIGH IN THE E GULF OF MEXICO NEAR 27N83W.
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 E CUBA NEAR 21N76W TO 25N75W TO 29N75W. FARTHER
TO THE E...A SURFACE TROUGH OVER THE CENTRAL ATLC EXTENDS FROM
29N46W TO A 1011 MB SURFACE LOW NEAR 22N48W TO 18N48W. LOW LEVEL
CONVERGENCE ASSOCIATED WITH THIS SURFACE TROUGH IS RESULTING IN
ISOLATED SHOWERS WITHIN 90 NM EITHER SIDE OF THIS FEATURE. THIS
SHOWER ACTIVITY IS BEING ENHANCED BY ATMOSPHERIC INSTABILITY IN
THE VICINITY OF AN UPPER TROUGH WITH AN AXIS EXTENDING FROM
14N58W TO 24N44W TO 32N40W TO N OF THE DISCUSSION AREA.
ALSO...UPPER LEVEL DIVERGENCE ASSOCIATED WITH AN 70-80-KT UPPER
LEVEL JET MAXIMUM E OF THE UPPER TROUGH AXIS IS SUPPORTING
NUMEROUS SHOWERS FROM 22N-30N BETWEEN 35W-42W. ACROSS THE E
ATLC...SUBSIDENCE ASSOCIATED WITH A SURFACE RIDGE EXTENDING
SOUTHWESTWARD FROM A 1038 MB SURFACE HIGH NEAR 46N4W IS
GENERALLY INHIBITING DEEP CONVECTION N OF 21N E OF 29W.
HOWEVER...ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER LOW
NEAR 33N18W IS RESULTING IN SCATTERED SHOWERS N OF 29N BETWEEN
15W-21W. ALSO...LOW LEVEL CONVERGENCE IS SUPPORTING ISOLATED
SHOWERS WITHIN 60 NM EITHER SIDE OF A SURFACE TROUGH EXTENDING
FROM 31N11W TO 32N10W TO NE OF THE DISCUSSION AREA. FARTHER TO
THE S...A SURFACE TROUGH EXTENDS FROM 14N48W TO 10N50W TO
6N52W...WITH SURFACE OBSERVATIONS INDICATING CYCLONIC CURVATURE
IN THE SURFACE WIND FIELD IN THE VICINITY OF THIS SURFACE
TROUGH. LOW LEVEL CONVERGENCE NEAR THIS SURFACE TROUGH IS
RESULTING IN SCATTERED SHOWERS FROM 7N-15N BETWEEN
46W-55W...WHICH ARE BEING ENHANCED BY UPPER LEVEL DIVERGENCE.
ALSO...A SURFACE TROUGH...EXTENDING FROM 12N33W TO 8N35W TO
4N36W...IS EMBEDDED WITHIN THE ITCZ...WITH LOW LEVEL CONVERGENCE
SUPPORTING SCATTERED MODERATE CONVECTION WITHIN 180 NM EITHER
SIDE OF THIS SURFACE TROUGH N OF 8N. AN UPPER RIDGE IS S OF
16N BETWEEN THE AFRICAN COAST AND 40W. UPPER LEVEL DIFFLUENCE
ASSOCIATED WITH THIS UPPER RIDGE IS ENHANCING THE CONVECTION
ASSOCIATED WITH THE ITCZ E OF 40W.

$$
COHEN




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