[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 201225 CCA
TWDAT

TROPICAL WEATHER DISCUSSION...CORRECTION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT MON OCT 20 2008

...CORRECTION FOR DATE...

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
1015 UTC.

...SPECIAL FEATURES...
A 1011 MB SURFACE LOW IS CENTERED IN THE NW CARIBBEAN NEAR
17N87W...OR ABOUT 90 NM E OF THE COAST OF BELIZE. BROAD LOW
LEVEL CONVERGENCE AROUND THE LOW...COUPLED WITH UPPER LEVEL
DIVERGENCE OVER THE NW CARIBBEAN...IS SUPPORTING SCATTERED
MODERATE/ISOLATED STRONG CONVECTION MAINLY TO THE E AND SE OF
THE LOW...FROM 14N-20N BETWEEN 80W-87W. SOME SLOW DEVELOPMENT OF
THIS SYSTEM IS POSSIBLE BEFORE IT MOVES INLAND OVER BELIZE OR
THE YUCATAN PENINSULA IN A DAY OR TWO. REGARDLESS OF
DEVELOPMENT...LOCALLY HEAVY RAINFALL IS EXPECTED OVER PORTIONS
OF HONDURAS...GUATEMALA...BELIZE...AND THE YUCATAN PENINSULA
OVER THE NEXT COUPLE OF DAYS.

...TROPICAL WAVES...
TROPICAL WAVE IS ALONG 44W S OF 18N MOVING W 10-15 KT.
SATELLITE IMAGERY DEPICTS INVERTED-V SIGNATURE IN CLOUD
COVERAGE...ALONG WITH COUNTERCLOCKWISE MOTION OF CLOUD ELEMENTS
IN THE VICINITY OF THE WAVE AXIS. CIMSS WAVETRAK PRODUCT
CONFIRMS PRESENCE OF LOW LEVEL COUNTERCLOCKWISE CIRCULATION NEAR
WAVE AXIS. THIS WAVE ALSO COINCIDES WITH A BROAD WESTWARD-MOVING
DEEP LAYER MOISTURE SURGE BASED ON TOTAL PRECIPITABLE WATER
PRODUCT FROM CIMSS. SCATTERED MODERATE CONVECTION IS FROM
14N-24N BETWEEN 36W-43W...WHICH IS BEING DRAWN NORTHWESTWARD ON
THE NE PERIPHERY OF AN UPPER LOW CENTERED NEAR 20N49W.
ALSO...SCATTERED MODERATE CONVECTION IS FROM 10N-14N BETWEEN
44W-52W.

TROPICAL WAVE IS ALONG 66W S OF 14N MOVING W 10-15 KT. WAVE IS
NOT PARTICULARLY WELL-DEFINED BASED ON SATELLITE IMAGERY...
THOUGH WEAK COUNTERCLOCKWISE CURVATURE IS DEPICTED IN SURFACE
WIND OBSERVATIONS NEAR WAVE AXIS. SCATTERED MODERATE/ISOLATED
STRONG CONVECTION IS WITHIN 180 NM W OF WAVE AXIS N OF
10N...WHICH IS BEING ENHANCED BY LOW LEVEL CONVERGENCE NEAR THE
ITCZ. ALSO...SCATTERED MODERATE CONVECTION IS FROM 5N-9N BETWEEN
63W-66W.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N16W 7N29W 8N42W 10N50W 10N62W.
CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION ARE
NOW W OF THE W AFRICAN COAST FROM 7N-13N BETWEEN 16W-22W.
ALSO...ISOLATED MODERATE CONVECTION IS FROM 2N-7N BETWEEN
22W-29W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER TROUGH AXIS EXTENDS FROM THE CENTRAL FLORIDA PENINSULA
TO THE BAY OF CAMPECHE...WHICH IS SUPPORTING A COLD FRONT THAT
EXTENDS FROM NW CUBA NEAR 23N80W TO 22N85W TO THE YUCATAN
PENINSULA NEAR 21N88W. A STATIONARY FRONT THEN EXTENDS FROM
21N88W TO THE SE BAY OF CAMPECHE NEAR 19N91W. THE PORTION OF
THIS COLD FRONT THAT WAS PREVIOUSLY STATIONARY IS SHOWING SIGNS
OF SOUTHWARD PROGRESSION AS EVIDENT IN PROGRESSION OF THE LOW
LEVEL THERMAL/MOISTURE GRADIENT AND CORRESPONDING CLOUD BANDS.
WEAK ATMOSPHERIC LIFT IN RELATIVELY MOIST SOUTHWESTERLY FLOW
ALOFT IS SUPPORTING ISOLATED SHOWERS WITHIN 60 NM EITHER SIDE OF
THE COLD FRONT AND STATIONARY FRONT...IMPACTING PORTIONS OF THE
SE GULF. FARTHER TO THE NW...AN UPPER RIDGE AXIS STRETCHES FROM
S TEXAS TO THE S APPALACHIANS. SUBSIDENCE AND DRY AIR IN NW FLOW
ALOFT BETWEEN THIS UPPER RIDGE AND THE AFOREMENTIONED UPPER
TROUGH ARE RESULTING IN FAIR WEATHER ACROSS MUCH OF THE NW AND
CENTRAL GULF...ESPECIALLY AS A SURFACE RIDGE EXTENDS INTO THE N
GULF FROM THE SE CONUS. ADDITIONALLY...WITH A SURFACE RIDGE
PRESENT OVER MEXICO...AND A 1011 MB SURFACE LOW OFF THE COAST OF
W MEXICO NEAR 12N94W...STRONG WINDS CONTINUE TO BLOW THROUGH THE
ISTHMUS OF TEHUANTEPEC RESULTING IN GALE FORCE WINDS IN THE
NEARBY E PACIFIC REGION.

CARIBBEAN SEA...
MOIST SW FLOW ALOFT E OF THE UPPER TROUGH AXIS IN THE GULF OF
MEXICO CONTINUES TO MOVE OVER THE NW CARIBBEAN...WHERE UPPER
LEVEL DIVERGENCE CONTINUES TO SUPPORT CONVECTION. THIS
CONVECTION IS BEING ENHANCED BY BROAD SURFACE CONVERGENCE AROUND
A 1011 MB SURFACE LOW NEAR 17N87W. PLEASE SEE THE SPECIAL
FEATURES SECTION ABOVE FOR MORE INFORMATION ON THIS SYSTEM.
FARTHER TO THE E...SCATTERED MODERATE CONVECTION IS FROM 12N-20N
BETWEEN 75W-80W...AFFECTING PORTIONS OF JAMAICA. THIS CONVECTION
IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE NEAR AND N OF AN
UPPER RIDGE. THIS RIDGE EXTENDS FROM AN UPPER HIGH NEAR 16N70W
TO THE NW CARIBBEAN NEAR 16N82W. FARTHER TO THE E...CONVECTIVE
COVERAGE IS LIMITED AS A RESULT OF SUBSIDENCE AND DRY AIR NEAR
THE UPPER HIGH. HOWEVER...ISOLATED MODERATE CONVECTION IS
OCCURRING ACROSS THE SE CARIBBEAN IN THE VICINITY OF THE
TROPICAL WAVE ALONG 66W.

ATLANTIC OCEAN...
AN UPPER TROUGH IS OVER THE W ATLC...AND IS SUPPORTING A SURFACE
COLD FRONT THAT EXTENDS FROM 32N65W TO 26N70W TO NW CUBA NEAR
23N80W. THE PORTION OF THE COLD FRONT THAT WAS PREVIOUSLY
STATIONARY IS SHOWING SIGNS OF SOUTHEASTWARD PROGRESSION AS
EVIDENT IN PROGRESSION OF THE LOW LEVEL THERMAL/MOISTURE
GRADIENT AND CORRESPONDING CLOUD BANDS. ATMOSPHERIC LIFT IN
MOIST SOUTHWESTERLY FLOW ALOFT IS SUPPORTING ISOLATED SHOWERS
WITHIN 60 NM EITHER SIDE OF THE COLD FRONT...AS WELL AS
SCATTERED MODERATE CONVECTION FROM 21N-24N BETWEEN 69W-74W. TO
THE NW OF THE COLD FRONT...DEEP CONVECTION IS BEING SUPPRESSED
BY SUBSIDENCE IN NW FLOW ALOFT UPSTREAM OF THE UPPER TROUGH
AXIS. FARTHER TO THE E...A COMPACT UPPER LOW IS CENTERED NEAR
20N49W...AND AN UPPER HIGH IS CENTERED NEAR 22N37W. DEEP LAYER
SOUTHEASTERLY FLOW BETWEEN THESE FEATURES IS DRAWING DEEP LAYER
MOISTURE NORTHWESTWARD FROM THE TROPICAL WAVE ALONG 44W...
RESULTING IN SCATTERED MODERATE CONVECTION FROM 14N-24N BETWEEN
36W-43W. FARTHER TO THE E...A 1025 MB SURFACE HIGH IS CENTERED
NEAR 32N36W...AND A SURFACE RIDGE EXTENDS FROM THIS HIGH TO THE
S NEAR 12N30W...WITH SUBSIDENCE AND STABLE CONDITIONS AROUND THE
SURFACE HIGH AND SURFACE RIDGE PREDOMINATING OVER MUCH OF THE
E ATLC. ALSO...AN UPPER TROUGH IS PRESENT OVER THE NE ATLC N OF
22N AND E OF 23W...WITH DEEP LAYER DRY AIR EMBEDDED WITHIN THE
TROUGH PREVENTING DEEP CONVECTION NEAR THIS FEATURE.

$$
COHEN




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