[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 171743
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON SEP 17 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1735 UTC.

...SPECIAL FEATURES...

TROPICAL STORM NADINE IS CENTERED NEAR 32.9N 35.3W AT 17/1500
UTC OR ABOUT 585 MI...940 KM SW OF THE AZORES MOVING NE AT 15
KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 987 MB. MAXIMUM
SUSTAINED WIND SPEED IS 60 KT WITH GUSTS TO 75 KT. SCATTERED
WEAK TO MODERATE CONVECTION IS FROM 31N-37N BETWEEN 29W-39W. SEE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

TROPICAL WAVE MOVES ACROSS THE CENTRAL TROPICAL ATLC WITH AXIS
EXTENDING FROM 16N33W TO 10N37W MOVING W AT 10-15 KT. THIS WAVE
IS EMBEDDED WITHIN BROAD CYCLONIC FLOW AND ALIGNS WITH A SURGE
OF DEEP LAYER MOISTURE PRESENT IN TOTAL PRECIPITABLE WATER
IMAGERY. HOWEVER...THIS WAVE IS EMBEDDED IN DRY SAHARAN AIR
ALOFT...ALLOWING FOR ONLY A FEW ISOLATED SHOWERS IN THE VICINITY
OF THE WAVE AXIS.

TROPICAL WAVE APPROACHES THE LESSER ANTILLES ANALYZED FROM
18N56W TO 11N60W MOVING W AT 5-10 KT. A 1011 MB SURFACE LOW IS
EMBEDDED ALONG THE WAVE AXIS NEAR 14N59W. THE WAVE LIES WITHIN
AN AREA OF MAXIMUM MOISTURE EVIDENT IN TOTAL PRECIPITABLE WATER
IMAGERY. THE WAVE REMAINS VERY SHALLOW AND EXHIBITS A LACK OF
SIGNIFICANT DEEP CONVECTION WITH GLOBAL MODEL DATA INDICATING A
700 MB TROUGH AXIS FARTHER TO THE WEST OF THE WAVE AXIS ACROSS
THE EASTERN CARIBBEAN SEA. THEREFORE...THE CONVECTION ASSOCIATED
TO THIS SYSTEM IS AFFECTING THE ERN CARIBBEAN AND LESSER
ANTILLES FROM BARBADOS TO BARBUDA BETWEEN 59W-68W.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH AXIS IS ANALYZED FROM THE WEST AFRICAN COAST
OF GUINEA NEAR 10N14W ALONG 8N20W 10N30W 9N40W TO 10N46W.
SCATTERED WEAK TO MODERATE CONVECTION IS FROM 6N-10N BETWEEN
43W-47W...AS WELL AS FROM 3N-10N BETWEEN 26W AND THE COAST OF
WEST AFRICA.

...DISCUSSION...

GULF OF MEXICO...
WATER VAPOR IMAGERY INDICATES A VIGOROUS MIDDLE TO UPPER LEVEL
TROUGH MOVING ACROSS THE FAR NW GULF. THIS FEATURE SUPPORTS A
1006 MB LOW CENTERED NEAR 28N93W WITH A SURFACE TROUGH EXTENDING
SSW FROM THE LOW CENTER ALONG 25N95W TO NEAR 22N97W. DESPITE THE
LOCATION OF THE SURFACE LOW AND TROUGH...SCATTERED MODERATE TO
HEAVY SHOWERS AND THUNDERSTORMS ARE DISPLACED E OF THE SURFACE
FEATURES OVER THE COASTAL WATERS OF MISSISSIPPI AND EASTERN
LOUISIANA N OF 26N BETWEEN 87W-92W...WHERE MUCH OF THE LIFTING
DYNAMICS ASSOCIATED TO UPPER DIFFLUENCE IS LOCATED. ISOLATED
SHOWERS AND THUNDERSTORMS ARE ALSO WITHIN 100 NM E OF THE
SURFACE TROUGH. MOIST SOUTHERLY LOW-LEVEL FLOW IS ELSEWHERE
ACROSS THE ERN HALF OF THE GULF WITH A FEW LINES OF SCATTERED
SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS N OF 25N E OF 90W.
COMPUTER MODELS SUGGEST THE SURFACE LOW WILL MOVE NE OUT OF OUR
DISCUSSION AREA TONIGHT AND BECOME EMBEDDED WITHIN THE NEXT COLD
FRONT TO SWEEP FROM THE CENTRAL PLAINS INTO THE SE CONUS BY
EARLY TUESDAY. HOWEVER...WHILE STRONG SUBSIDENCE TAKES OVER THE
W AND NW BASINS...THE WEATHER ACROSS MUCH OF THE ERN HALF OF THE
GULF AND BAY OF CAMPECHE WILL REMAIN UNSETTLED AS SURFACE
TROUGHING LINGERS IN THIS REGION OVER THE NEXT 24-48 HOURS.

CARIBBEAN SEA...
THE MAIN REGION OF INTEREST REMAINS OVER THE ERN CARIBBEAN AS A
TROPICAL WAVE AND ASSOCIATED LOW PRESSURE SYSTEM SLOWLY TAKE
OVER THE LESSER ANTILLES PRODUCING SCATTERED HEAVY SHOWERS AND
ISOLATED THUNDERSTORMS OVER THIS GROUP OF ISLANDS AND PARTS OF
THE ERN CARIBBEAN FROM BARBADOS TO BARBUDA BETWEEN 59W-68W.
WHILE SURFACE TROUGHING REMAINS E OF THE ANTILLES WHERE THE WAVE
AND SURFACE LOW ARE LOCATED...MIDDLE TROUGHING IS NOTED ON MODEL
DATA AT 700 MB COVERING MUCH OF THE ERN CARIBBEAN E OF 68W. THE
OVERALL ACTIVITY WILL SLOWLY MOVE W ACROSS THE NRN ANTILLES AND
ERN CARIBBEAN DURING THE NEXT 24 HOURS. SCATTERED MODERATE
SHOWERS ARE NOTED WITHIN 50-80 NM OFF THE COAST OF PANAMA...
COSTA RICA...AND SRN NICARAGUA ASSOCIATED TO THE ERN PACIFIC
MONSOON TROUGH EXTENDING ACROSS CENTRAL AMERICA TO NRN
COLOMBIA. THE REMAINDER OF THE DISCUSSION AREA IS UNDER FAIR
WEATHER CONDITIONS RELATED TO DRY AIR AND MODERATE TO STRONG
SUBSIDENCE ALOFT...SUPPRESSING DEEP CONVECTION AND ONLY ALLOWING
FOR A FEW ISOLATED SHOWERS OVER THE NW BASIN.

ATLANTIC OCEAN...
A WEAK UPPER LEVEL TROUGH MOVING ACROSS THE FAR ERN GULF OF
MEXICO IS GENERATING SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS OVER THE NW BAHAMAS TO THE COAST OF THE FLORIDA
PENINSULA AND STRAITS S OF 27N W OF 77W. THIS AREA OF SHOWERS IS
EXPECTED TO LIFT N DROWN BY A FRONTAL SYSTEM MOVING FROM THE
CENTRAL PLAINS TO THE SE CONUS DURING THE NEXT 24 HOURS. AN
UPPER LEVEL LONGWAVE/TROUGH IS NOTED ON WATER VAPOR IMAGERY
MOVING INTO THE N-CENTRAL ATLC ALONG 50W N OF THE DISCUSSION
AREA. THIS FEATURE SUPPORTS A COLD FRONT EXTENDING INTO OUR AREA
AS A WEAK SURFACE TROUGH ALONG 31N56W TO NEAR 24N62W. THIS
BOUNDARY IS MOSTLY EMBEDDED WITH DRY AIR KEEPING SHOWER ACTIVITY
AT A MINIMUM. CURRENTLY...ISOLATED WEAK SHOWERS ARE NOTED WITHIN
20 NM E OF THE AXIS. THIS BOUNDARY IS EXPECTED TO WEAKEN AND
DISSIPATE DURING THE NEXT 24 HOURS...AS HIGH PRESSURE CONTINUES
TO BUILD OVER THE WRN ATLC THROUGH EARLY TUESDAY. TROPICAL STORM
NADINE IS APPROACHING THE ERN ATLC WATERS NEAR THE AZORES. SEE
SPECIAL FEATURE ABOVE FOR MORE DETAILS ON NADINE. A WEAK AREA OF
LOW-LEVEL CONVERGENCE IS NOTED S OF NADINE ANALYZED FROM 28N34W
TO 23N49W WITH VERY LITTLE ACTIVITY. OTHERWISE...THE REMAINDER
OF THE ATLC BASIN DISCUSSION AREA IS DOMINATED BY WEAK SURFACE
RIDGING AROUND A 1018 MB HIGH NEAR 26N23W. THE OVERALL FAIR
WEATHER IS ENHANCED ALOFT BY THICK LAYER OF SAHARAN DUST NOTED
ON METEOSAT-9 SAL PRODUCT E OF 40W.

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

$$

GARCIA




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