[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 180533
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 AM EST TUE NOV 18 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
0515 UTC.

...TROPICAL WAVES...
A TROPICAL WAVE IS OVER THE E CARIBBEAN ALONG 68W/69W S OF 18N
MOVING W 10-15 KT. A MAXIMUM IN DEEP LAYER MOISTURE COINCIDES
WITH THE WAVE AXIS BASED ON CIMSS TOTAL PRECIPITABLE WATER
PRODUCT. ALSO...CIMSS WAVETRAK PRODUCT INDICATES A MAXIMUM IN
LOW LEVEL CYCLONIC CIRCULATION ALONG THE WAVE AXIS. SCATTERED
SHOWERS ARE WITHIN 60 NM EITHER SIDE OF WAVE AXIS S OF 16N.

...THE ITCZ...
THE ITCZ AXIS IS ANALYZED ALONG 8N13W 7N22W 7N36W 7N44W 6N54W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 3N-12N
BETWEEN 19W-28W. SCATTERED MODERATE CONVECTION IS WITHIN 150 NM
N OF THE ITCZ AXIS BETWEEN 37W-42W.

...DISCUSSION...

GULF OF MEXICO...
A BROAD UPPER LEVEL TROUGH OVER THE E CONUS EXTENDS INTO THE
GULF...WITH WESTERLY FLOW ALOFT AND DEEP LAYER DRY AIR COVERING
MUCH OF THE GULF REGION. ALSO...A MODIFIED CONTINENTAL POLAR
AIRMASS PERSISTS ACROSS THE GULF REGION. AS A RESULT...
TEMPERATURES ACROSS THE GULF REGION ARE BELOW SEASONAL AVERAGES.
THIS RELATIVELY COOLER AND DRIER AIRMASS IS BEING SUPPORTED BY A
1028 MB SURFACE HIGH CENTERED OVER SE TEXAS...WITH AN ASSOCIATED
SURFACE RIDGE EXTENDING INTO THE W GULF. AS THE COOLER AIR IS
BEING ADVECTED OVER THE RELATIVELY WARMER GULF WATERS...WEAK LOW
LEVEL INSTABILITY IS SUPPORTING STRATOCUMULUS CLOUDS S OF 25N
ACROSS THE GULF. HOWEVER...SUBSIDENCE AND STABLE ATMOSPHERIC
CONDITIONS HIGHER IN THE ATMOSPHERE ARE INHIBITING DEEP
CONVECTION ACROSS THE GULF REGION. THE AFOREMENTIONED BROAD
UPPER TROUGH IS ALSO SUPPORTING A REINFORCING SURFACE FRONT
FURTHER NORTH. THIS FRONT IS CURRENTLY DRAPED FROM THE SE CONUS
INTO THE PLAINS OF THE CONUS AND THEN NORTHWARD ACROSS THE
NORTHERN ROCKY MOUNTAINS. AS THE ASSOCIATED UPPER LEVEL ENERGY
TRANSLATES SOUTHEASTWARD...THE SURFACE FRONT WILL MOVE
SOUTHEASTWARD AS A COLD FRONT ACROSS THE CENTRAL AND E GULF OVER
THE NEXT DAY. AN EVEN COOLER AND DRIER AIRMASS IS IN THE WAKE OF
THIS FRONT...WITH FREEZE WATCHES IN EFFECT ACROSS PORTIONS OF
THE SE CONUS ALONG THE GULF COAST FOR TUESDAY NIGHT.
ADDITIONALLY...STRONG N TO NE SURFACE WINDS ARE BLOWING THROUGH
THE ISTHMUS OF TEHUANTEPEC RESULTING IN GALE FORCE WINDS IN THE
E PACIFIC REGION...WHICH ARE FORECAST TO BECOME STORM FORCE AT
19/0000 UTC.

CARIBBEAN SEA...
ACROSS THE NW CARIBBEAN...A SURFACE STATIONARY FRONT EXTENDS
FROM E CUBA NEAR 21N76W TO 17N81W TO CENTRAL NICARAGUA NEAR
12N85W. LOW LEVEL CONVERGENCE NEAR THIS FRONT IS INTERACTING
WITH DEEP MOISTURE OVER THE W CARIBBEAN TO GENERATE SCATTERED
SHOWERS AND THUNDERSTORMS FROM 11N-18N BETWEEN 78W-84W. THIS
ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIVERGENCE IN THE
VICINITY OF AN UPPER RIDGE PRESENT OVER THE W CARIBBEAN...WITH
THE AXIS OF THE UPPER RIDGE EXTENDING FROM NW VENEZUELA NEAR
10N71W TO 15N79W TO 20N84W. OVER THE E CARIBBEAN...AN UPPER
LEVEL TROUGH IS PRESENT...WITH UPPER LEVEL DIVERGENCE IN MOIST
SOUTHWESTERLY FLOW ALOFT SUPPORTING SCATTERED SHOWERS OVER THE
E CARIBBEAN S OF 16N E OF 73W. THIS ACTIVITY IS BEING ENHANCED
BY THE TROPICAL WAVE ALONG 68W/69W.

ATLANTIC OCEAN...
A BROAD UPPER TROUGH IS OVER THE E CONUS AND THE W ATLC...WHICH
IS SUPPORTING A SURFACE STATIONARY FRONT THAT EXTENDS FROM
E CUBA NEAR 21N76W TO 26N69W TO 32N63W TO NE OF THE DISCUSSION
AREA. ISOLATED SHOWERS ARE WITHIN 60 NM EITHER SIDE OF THIS
STATIONARY FRONT...WITH THE COVERAGE OF THIS ACTIVITY BEING
LIMITED AS THE STRONGEST UPPER LEVEL ENERGY REMAINS N OF THE
DISCUSSION AREA. TO THE W OF THIS STATIONARY FRONT...A MODIFIED
CONTINENTAL POLAR AIRMASS IS IN PLACE...WITH TEMPERATURES BELOW
SEASONAL AVERAGES ACROSS THE FLORIDA PENINSULA. FARTHER TO THE
E...A 1018 MB SURFACE HIGH IS CENTERED NEAR 29N56W...WHICH IS
BEING SUPPORTED BY A SHARP UPPER LEVEL RIDGE WITH AN AXIS
EXTENDING FROM 24N57W TO 29N54W TO 32N54W TO NE OF THE
DISCUSSION AREA. TO THE E...AN UPPER LOW IS CENTERED NEAR 31N37W
THAT IS ACCOMPANIED BY AN UPPER TROUGH N OF 18N BETWEEN 27W-45W.
THE UPPER LOW AND UPPER TROUGH ARE ACCOMPANIED BY A SURFACE LOW
AND TWO SURFACE TROUGHS. ONE SURFACE TROUGH EXTENDS FROM A 1004
MB SURFACE LOW NEAR 32N40W TO 27N39W TO 23N39W...WITH SCATTERED
SHOWERS N OF 26N BETWEEN 36W-42W. THE SECOND SURFACE TROUGH
EXTENDS FROM 31N30W TO 26N31W TO 22N34W...WITH SCATTERED SHOWERS
AND THUNDERSTORMS WITHIN 90 NM EITHER SIDE OF THIS SECOND
SURFACE TROUGH. THE ACTIVITY ASSOCIATED WITH THE SECOND SURFACE
TROUGH IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE IN
SOUTHWESTERLY FLOW ALOFT BETWEEN THE ACCOMPANYING UPPER
TROUGH...AND AN UPPER RIDGE THAT IS N OF 19N BETWEEN THE AFRICAN
COAST AND 27W. OVER THE TROPICAL ATLC...AN UPPER RIDGE IS S OF
10N BETWEEN THE AFRICAN COAST AND 27W...WITH ANOTHER UPPER RIDGE
PRESENT S OF 6N BETWEEN 30W-38W. UPPER LEVEL DIVERGENCE IN THE
VICINITY OF THESE UPPER RIDGES IS ENHANCING THE CONVECTION
ASSOCIATED WITH THE ITCZ.

$$
COHEN



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