[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 271737
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT FRI JUL 27 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
1645 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS MOVING W AT 15-20 KT THROUGH THE CENTRAL TRPCL
ATLC ALONG 20N36W TO 10N37W. TOTAL PRECIPITABLE WATER IMAGERY
INDICATES THAT THE WAVE LIES WITHIN A SURGE OF DEEP LAYER
MOISTURE. THERE IS ALSO A CLEARING IN THE WIDESPREAD SAHARAN AIR
LAYER THAT IS PRESENT ACROSS MUCH OF THE TROPICAL ATLC. A RECENT
ASCAT SCATTEROMETER PASS ALSO INDICATES THAT THERE IS LOW-LEVEL
CYCLONIC FLOW AROUND THE AXIS. DUE TO THE LARGE AROUND OF DUST
NEAR THE WAVE...MOST DEEP CONVECTION IS SUPPRESSED EXCEPT FOR
AREAS WITHIN THE MONSOON TROUGH WHERE SCATTERED MODERATE
CONVECTION IS FROM 7N-10N BETWEEN 36W-45W.

TROPICAL WAVE IS APPROACHING THE LESSER ANTILLES MOVING W AT
15-20 KT CURRENTLY ALONG 21N54W TO 11N55W. THE WAVE PREVIOUSLY
EXTENDING MORE TOWARDS THE NORTH...BUT IT APPEARS THAT THE NRN
PORTION WILL MOVE NW WHILE THE SRN PORTION WILL CONTINUE W. FOR
THIS REASON...THE WAVE HAS BEEN SPLIT SO THAT THE NRN PORTION
WILL CONTINUE AS A SURFACE TROUGH. THE WAVE LIES ON THE W SIDE
OF A SURGE OF DEEP LAYER MOISTURE PRESENT IN TOTAL PRECIPITABLE
WATER IMAGERY. DUE TO DUST SURROUNDING THE WAVE...ONLY ISOLATED
MODERATE CONVECTION IS NEAR THE ITCZ REGION FROM 7N-11N BETWEEN
53W-57W.

TROPICAL WAVE IS MOVING W OFF THE YUCATAN PENINSULA ALONG 22N89W
TO 16N91W AT 15 KT. TOTAL PRECIPITABLE WATER IMAGERY INDICATES
THAT THE WAVE LIES IN THE MIDDLE OF A SURGE OF DEEP LAYER
MOISTURE THAT EXTENDS FROM THE FAR NW CARIBBEAN INTO THE SW GULF
OF MEXICO. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS E OF
THE WAVE AXIS FROM 16N-21N BETWEEN 87W-90W.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS W AFRICA TO THE COAST OF
SENEGAL AT 14N17W CONTINUING ACROSS ATLC WATERS ALONG 12N29W
9N40W 11N47W. THE ITCZ BEGINS AT 10N47W AND CONTINUES TO 9N61W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 7N-11N
BETWEEN 16W-23W...AND FROM 7N-10N BETWEEN 26N-32N.

...DISCUSSION...

GULF OF MEXICO...
THE NRN GULF OF MEXICO IS EXPERIENCING SCATTERED
SHOWERS/THUNDERSTORMS N OF 28N BETWEEN 84W-92W...DUE TO
DIFFLUENCE ALOFT NEAR THE NRN EXTENT OF AN INVERTED UPPER LEVEL
TROUGH THAT EXTENDS FROM THE WRN FLORIDA PANHANDLE TO THE
YUCATAN PENINSULA. THE REMAINDER OF THE BASIN IS EXPERIENCING
MOSTLY FAIR CONDITIONS DUE TO DRY AIR ALOFT AROUND AN UPPER
LEVEL RIDGE CENTERED IN THE W ATLC. THE UPPER RIDGE SUPPORTS
SURFACE RIDGING ACROSS THE BASIN ALONG 27N. A FEW HEAVY SHOWERS
HAVE POPPED UP OVER W CENTRAL FLORIDA. SHOWERS/THUNDERSTORMS ARE
ALSO OVER THE YUCATAN PENINSULA ASSOCIATED WITH A TROPICAL WAVE
ABOUT TO MOVE INTO THE SW GULF. SEE TROPICAL WAVE SECTION ABOVE
FOR MORE DETAILS. LIGHT ANTI-CYCLONIC FLOW IS AROUND THE SURFACE
RIDGE. EXPECT THE TROPICAL WAVE TO MOVE ACROSS THE SW GULF WITH
POSSIBLE SHOWERS/THUNDERSTORMS ALONG IT. THE REMAINDER OF THE
BASIN WILL REMAIN UNDER SURFACE RIDGING WITH
SHOWERS/THUNDERSTORMS LIKELY ACROSS THE NRN GULF.

CARIBBEAN SEA...
THE ENTIRE CARIBBEAN IS MOSTLY DRY TODAY AS IT IS IMPACTED WITH
SAHARAN DUST AND DRY AIR ALOFT. AN INVERTED UPPER TROUGH OVER
THE YUCATAN PENINSULA HAD FLARED UP SOME STORMS OVER THE NW
WATER...WHICH HAVE NOW DISSIPATED. AN UPPER LEVEL RIDGE COVERS
THE SW CARIBBEAN...AS WELL AS THE FAR ERN CARIBBEAN. A DRY UPPER
LEVEL LOW IS ACROSS THE N CENTRAL CARIBBEAN ACROSS THE WINDWARD
PASSAGE. TRADEWIND FLOW OF 15-20 KTS IS ACROSS MUCH OF THE BASIN
WITH ONLY A FEW ISOLATED LOW-LEVEL SHOWERS EMBEDDED WITHIN THE
FLOW. A FEW ISOLATED SHOWERS/THUNDERSTORMS ARE ALSO OVER
PORTIONS OF NICARAGUA AND COSTA RICA. EXPECT LITTLE CHANGE FOR
THE NEXT 24 HOURS. A TROPICAL WAVE APPROACHING THE LESSER
ANTILLES SHOULD REACH THE ERN CARIBBEAN WITHIN THE NEXT 24-36
HOURS.

ATLANTIC OCEAN...
A LARGE UPPER LEVEL RIDGE COVERS THE W ATLC CENTERED NEAR 33N68W
SUPPORTING A 1020 MB HIGH NEAR 26N70W. MOSTLY FAIR WEATHER IS
ACROSS THIS AREA DUE TO AN AREA OF SAHARAN DUST THAT IS ALSO
PRESENT ACROSS THE CARIBBEAN. A WEAK 1016 MB LOW IS JUST N OF
THE DISCUSSION AREA NEAR 32N61W. A STATIONARY FRONT EXTENDS FROM
THE LOW CENTER ALONG 30N60W 28N67W 31N71W. SCATTERED
SHOWERS/ISOLATED THUNDERSTORMS ARE WITHIN 120 NM SW OF THE AXIS.
FARTHER E...A SURFACE TROUGH IS ALONG 27N48W TO 24N53W. THE
TROUGH IS ACTUALLY A SPLIT OFF PORTION OF A TROPICAL WAVE TO THE
S. DUE TO THE LARGE AREA OF SAHARAN DUST...NO SHOWERS OR
THUNDERSTORMS ARE NEAR THE TROUGH. THE REMAINDER OF THE BASIN IS
DOMINATED BY SURFACE RIDGING AROUND A 1026 MB HIGH NEAR 34N40W.
THE RIDGE...IN COMBINATION WITH THE SAHARAN AIR LAYER IS
MAINTAINING FAIR CONDITIONS BASIN-WIDE. ALOFT...AN UPPER LEVEL
LOW IS CENTERED NEAR 24N58W...BUT IS NOT CAUSING ANY WEATHER. A
PAIR OF UPPER RIDGES COVER THE TROPICAL ATLC CENTERED NEAR
19N46W AND 18N20W. A BROAD UPPER TROUGH IS BETWEEN THEM ALONG
30W.

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

$$
WALTON





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