[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 182347
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST SUN NOV 18 2012

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.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS ACROSS WEST AFRICA TO THE COAST OF
GUINEA-BISSAU AT 12N16W TO 8N21W. THE ITCZ BEGINS AT 8N21W AND
CONTINUES ALONG 6N29W 8N43W 8N59W. SCATTERED MODERATE CONVECTION
IS FROM 5N-7N BETWEEN 15W-17W. ISOLATED MODERATE/STRONG
CONVECTION IS FROM 5N-8N BETWEEN 28W-31W.

...DISCUSSION...

GULF OF MEXICO...
MAINLY NORTHWESTERLY FLOW ALOFT CONTINUES TO COVER THE GULF OF
MEXICO BETWEEN AN UPPER LEVEL RIDGE WITH AXIS FROM THE SW GULF
NEAR 20N96W TO THE MISSISSIPPI VALLEY...AND AN UPPER LEVEL
TROUGH EXTENDING FROM THE MID-ATLANTIC STATES THROUGH THE
FLORIDA PENINSULA INTO THE NW CARIBBEAN. WATER VAPOR IMAGERY
INDICATES MOSTLY DRY AIR IS BEING DRAWN OVER THE BASIN IN THE
UPPER LEVELS. THIS...ALONG WITH SURFACE RIDGING ACROSS THE
WESTERN GULF IS HELPING PROVIDING MOSTLY FAIR CONDITIONS AT THE
SURFACE. HOWEVER...A SURFACE TROUGH EXTENDS FROM THE CENTRAL
GULF INTO THE SE GULF ALONG 27N89W TO 20N84W. ISOLATED SHOWERS
ARE WITHIN 150 NM TO EITHER SIDE OF THE AXIS. CYCLONIC WINDS OF
15-20 KT ARE ACROSS THE EASTERN GULF AROUND THE SURFACE TROUGH.
ISOLATED SHOWERS ARE ALSO NOTED IN THE EXTREME SW GULF NEAR THE
COAST OF MEXICO. THE SURFACE TROUGH IS EXPECTED TO DRIFT WEST
SLOWLY OVER THE NEXT FEW DAYS WITH SURFACE RIDGING REMAINING
ELSEWHERE. MOISTURE AND POSSIBLE SHOWERS WILL ACCOMPANY THE
TROUGH.

CARIBBEAN SEA...
THE UPPER LEVEL TROUGH OVER THE FAR EASTERN GULF CONTINUES SOUTH
INTO THE NW CARIBBEAN ACCOMPANIED BY DRY AIR ALOFT...WHICH IS
PROVIDING MOSTLY FAIR CONDITIONS ACROSS THIS PORTION OF THE
BASIN. A FEW ISOLATED SHOWERS ARE JUST EAST OF THE YUCATAN
PENINSULA ASSOCIATED WITH A SURFACE TROUGH THAT EXTENDS THROUGH
THE YUCATAN CHANNEL TO NEAR 20N84W. MOIST SOUTHWESTERLY FLOW AND
DIFFLUENCE ALOFT BETWEEN THE UPPER TROUGH AND AN UPPER LEVEL
RIDGE OVER THE EASTERN CARIBBEAN ALONG 66W ARE GENERATING A
LARGE AREA OF SHOWERS/ISOLATED THUNDERSTORMS OVER THE CENTRAL
CARIBBEAN FROM 11N-15N BETWEEN 77W-83W...AND FROM 14N-17N
BETWEEN 70W-77W. A FEW SHOWERS/THUNDERSTORMS ARE ALSO TO THE
NORTH OVER HISPANIOLA AND PUERTO RICO. SOME OF THE ACTIVITY IN
THE SW CARIBBEAN IS ASSOCIATED WITH THE MONSOON TROUGH THAT
EXTENDS THROUGH SOUTHERN COSTA RICA TO A 1010 MB SURFACE LOW
NORTH OF PANAMA NEAR 10N78W. A CLUSTER OF SHOWERS/THUNDERSTORMS
IS SOUTH OF THE LOW CENTER INTO COASTAL PANAMA. THE REMAINDER OF
THE EASTERN CARIBBEAN IS UNDER FAIR CONDITIONS ASSOCIATED WITH
DRY AIR ALOFT AROUND THE UPPER RIDGE. EXPECT LITTLE CHANGE OVER
THE NEXT COUPLE OF DAYS.

ATLANTIC OCEAN...
AN UPPER LEVEL LOW JUST OFFSHORE OF SOUTH CAROLINA SUPPORTS A
WEAK 1015 MB SURFACE LOW NEAR 32N79W FROM WHICH A STATIONARY
FRONT EXTENDS SOUTH ALONG 30N77W 27N78W. CURRENTLY...NO SHOWERS
ARE ASSOCIATED WITH THE FRONT IN THE DISCUSSION AREA.
HOWEVER...A FEW SHOWERS ARE SOUTH OF THE BOUNDARY JUST OFF THE
SE COAST OF FLORIDA. FARTHER EAST...DIFFLUENCE ALOFT BETWEEN THE
UPPER LOW/TROUGH AND AN UPPER LEVEL RIDGE EXTENDING FROM THE
EASTERN CARIBBEAN INTO THE THE CENTRAL ATLC IS HELPING SUPPORT
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS NORTH OF 289N BETWEEN
67W-71W...AND FROM 21N-24N BETWEEN 61W-65W. ISOLATED SHOWERS ARE
POSSIBLE ELSEWHERE NORTH OF 21N BETWEEN 54W-68W. A PAIR OF
SURFACE TROUGHS ARE EMBEDDED WITHIN THIS LARGE ARE OF DIFFLUENCE
ALOFT. THE FIRST IS ALONG 28N69W TO 21N70W WITH ONLY THE AREA OF
SHOWERS/THUNDERSTORMS TO THE NORTH AS PREVIOUSLY DESCRIBED. THE
SECOND IS ALONG 31N59W TO 28N64W. DUE TO DENSE HIGH LEVEL
CLOUDS...IT IS DIFFICULT TO TELL IF ANY SHOWERS ARE NEAR THE
AXIS AT THE SURFACE. THE UPPER LEVEL RIDGE ACROSS THE CENTRAL
ATLC CONTINUES TOWARDS THE NE WHERE IT BECOMES FLATTENED BY A
LARGE LONGWAVE UPPER TROUGH OVER THE NORTHERN ATLC. THE RIDGE
STILL SUPPORTS A BROAD SURFACE RIDGE ACROSS THE SE ATLC ANCHORED
BY A PAIR OF 1022 AND 1023 MB HIGH CENTERS NEAR 31N39W AND
32N27W RESPECTIVELY. AN UPPER LEVEL LOW NEAR 17N43W...JUST EAST
OF THE MAIN UPPER RIDGE...SUPPORTS A SURFACE TROUGH THAT EXTENDS
INTO THE SURFACE RIDGE ALONG 18N40W TO 12N44W. SCATTERED
SHOWERS/POSSIBLE THUNDERSTORMS ARE FROM 14N-23N BETWEEN 30W-40W.

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

$$
WALTON





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