[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 260005
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED SEP 25 2013

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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL
ANALYSIS.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...TROPICAL WAVES...
A WEAK TROPICAL WAVE AXIS EXTENDS FROM 18N39W TO 09N36W MOVING
WEST NEAR 15 KT. TOTAL PRECIPITABLE WATER AND WATER VAPOR
IMAGERY SHOW THE WAVE IS EMBEDDED IN A MODERATE MOIST
ENVIRONMENT. GLOBAL MODEL GUIDANCE SUGGEST A WAVE AXIS AT 700 MB
HOWEVER LATEST PASSES OF ASCAT AND OSCAT REFLECT NO WAVE SIGNAL
AT THE SURFACE. IN THE NORTHERN SECTOR OF THE WAVE THERE IS SOME
SAHARAN DRY AIR INHIBITING CONVECTION WHILE SCATTERED MODERATE
CONVECTION IS FROM 08N-13N BETWEEN 33W-40W. HOWEVER THIS
PRECIPITATION APPEARS TO BE TRAILING CONVECTION FROM THE
TROPICAL WAVE AHEAD OF IT.

A TROPICAL WAVE AXIS EXTENDS FROM 18N51W TO 10N47W AND MOVES
WEST NEAR 15 KT. TOTAL PRECIPITABLE WATER OR TPW IMAGERY SHOW
THE WAVE IS EMBEDDED IN A MODERATE TO HIGH MOIST ENVIRONMENT. A
CLUSTER OF MODERATE CONVECTION IS IN THE SOUTHERN SECTOR OF THE
WAVE FROM 09N-12N BETWEEN 44W-47W...COINCIDING WITH A REGION OF
MAXIMUM MOISTURE IN THE TPW. SCATTERED MODERATE CONVECTION IS
ELSEWHERE FROM 09N-18N BETWEEN 40W-49W. THIS CONVECTION IS BEING
SUPPORTED BY AN UPPER-LEVEL LOW CENTERED NEAR 20N50W AND LOW
VALUES OF DEEP LAYER ENVIRONMENTAL WIND SHEAR.

A TROPICAL WAVE AXIS EXTENDS FROM 21N58W TO 14N59W AND MOVES W-
NW NEAR 15 KT. TOTAL PRECIPITABLE WATER AND WATER VAPOR IMAGERY
SHOW THE WAVE CONTINUES EMBEDDED IN A VERY DRY AIR ENVIRONMENT
WHICH IS SUPPRESSING CONVECTION.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH AXIS PASSES THROUGH WEST AFRICA NEAR 09N13W
TO 07N26W. THE ITCZ CONTINUES FROM 07N26W TO 09N40W TO 05N49W.
SCATTERED MODERATE CONVECTION IS FROM 04N-11N BETWEEN 16W-22W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL TROUGH AXIS EXTENDS FROM OVER THE SE CONUS SW TO
A BROAD BASE OVER THE WESTERN GULF. WATER VAPOR IMAGERY
INDICATES THIS TROUGH AXIS DELINEATES A MOIST AND DIFFLUENT
ATMOSPHERE TO THE EAST AND VERY DRY AND SUBSIDENT ATMOSPHERE TO
THE WEST. THIS UPPER LEVEL TROUGH SUPPORTS A 1008 MB LOW
CENTERED NEAR 27N91W WITH A SURFACE TROUGH ANALYZED FROM 28N86W
TO THE LOW TO 25N94W. A STATIONARY FRONT EXTENDS EAST FROM A
1007 MB LOW OVER THE FLORIDA PANHANDLE TO A 1006 MB LOW OVER THE
SW NORTH ATLC REGION NEAR 30N76W. A COLD FRONT EXTENDS SW FROM
THE LOW OVER THE FLORIDA PANHANDLE TO 28N90W 27N95W. SCATTERED
SHOWERS AND ISOLATED TSTMS ARE OCCURRING ACROSS THE EASTERN GULF
WATERS FROM 25N-29N EAST OF 86W AS WELL AS IN PORTIONS OF THE
NORTHERN FLORIDA PENINSULA CLOSER TO THE FRONTAL BOUNDARY.
ISOLATED SHOWERS REMNANTS OF A SURFACE TROUGH PREVIOUSLY OVER
THE BAY OF CAMPECHE ARE SOUTH OF 22N EAST OF 95W.

WITHIN A 24 HOUR PERIOD...THE COLD FRONT WILL OVERTAKE THE
SURFACE TROUGH AND THEN WILL CONTINUE TO MOVE SE AS A HIGH
PRESSURE CENTER DEVELOPS IN THE NW GULF. THE COLD FRONT IS
EXPECTED TO MOVE ACROSS SOUTHERN FLORIDA BY FRIDAY AFTERNOON AND
BE OFF GULF WATERS EARLY ON SATURDAY.

CARIBBEAN SEA...
EXCEPT FOR THE SOUTHERN CARIBBEAN...THE WINDWARD PASSAGE AND
SOUTHERN CUBA...DRY AIR SUBSIDENCE DOMINATES ACROSS THE BASIN
SUPPORTING FAIR WEATHER. AN UPPER LEVEL ANTICYCLONE IS CENTERED
OVER THE BAHAMAS IN THE SW NORTH ATLC AND IS PROVIDING MUCH OF
THE CENTRAL AND WESTERN CARIBBEAN WITH NORTHEASTERLY FLOW ALOFT.
IN THE SW CARIBBEAN...AN INVERTED TROUGH IS NOTED ON WATER VAPOR
IMAGERY. GIVEN THE LOW-LEVEL MOISTURE CONVERGENCE DUE TO
EASTERLY TRADES AND THE UPPER LEVEL LIFTING DYNAMICS
...SCATTERED MODERATE CONVECTION AND TSTMS ARE OCCURRING S OF
14N WEST OF 78W AND S OF 11N EAST OF 78W. THIS CONVECTION LIKELY
ENHANCED DUE TO THE CLOSE PROXIMITY OF THE MONSOON TROUGH AXIS
EXTENDS INLAND PANAMA...COSTA RICA...AND CENTRAL NICARAGUA.
ISOLATED SHOWERS AND TSTMS ARE JUST WEST OF JAMAICA FROM 17N-19N
EAST OF 80W.

A TROPICAL WAVE IS EXPECTED TO MOVE ACROSS THE LESSER ANTILLES
BY EARLY SATURDAY POSSIBLY ENHANCING SHOWERS IN THE EASTERN
CARIBBEAN.

HISPANIOLA...
CURRENTLY DRY AIR IS ACROSS THE EASTERN ISLAND SUPPORTING FAIR
WEATHER. HOWEVER...MODERATE MOISTURE IN THE WINDWARD PASSAGE
ALONG WITH A SECTOR OF MIDDLE-LEVEL DIFFLUENCE IN THE SAME
REGION IS SUPPORTING SHOWERS AND TSTMS OVER CENTRAL HAITI. IN
THE DAYS AHEAD...THE SOUTHERN EXTENT OF A WEAK TROPICAL WAVE
CURRENTLY ALONG 58W IS FORECAST TO CLIP ACROSS THE ISLAND
SATURDAY PROVIDING A POSSIBLE SLIGHT INCREASE IN CONVECTION
DURING THE AFTERNOON AND EVENING HOURS.

ATLANTIC OCEAN...
OVER THE SW NORTH ATLC...A STATIONARY FRONT EXTENDS WESTWARD
FROM A 1007 MB LOW NEAR 30N76W. A WARM FRONT EXTENDS EASTWARD
FROM THE LOW TO 29N68W WHERE IT TRANSITIONS TO A COLD FRONT NE
TO 30N60W. A PRE-FRONTAL TROUGH EXTENDS FROM 29N62W TO 25N67W.
SCATTERED SHOWERS ASSOCIATED WITH THESE FEATURES ARE N OF 23N
WEST OF 62W.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
NR


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