[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 202350
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT MON AUG 20 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.

...SPECIAL FEATURES...

THE CENTER OF POST-TROPICAL CYCLONE GORDON AT 20/2100 UTC IS
NEAR 39.2N 20.3W...OR ABOUT 320 NM ENE OF THE AZORES ISLANDS.
GORDON IS MOVING ENE AT 14 KNOTS. THE ESTIMATED MINIMUM CENTRAL
PRESSURE IS 1000 MB. THE MAXIMUM SUSTAINED WIND SPEED IS 40 KT
WITH GUSTS TO 50 KT. PLEASE READ THE NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC AND THE PUBLIC ADVISORY
UNDER MIATCPAT3/WTNT33 KNHC FOR MORE DETAILS. SCATTERED MODERATE
CONVECTION IS FROM 40N-42N BETWEEN 18W-21W.

TROPICAL WAVE EXTENDS FROM NEAR 22N45W TO A WELL-DEFINED 1009 MB
SURFACE LOW AT 16N47W. THE SYSTEM IS MOVING WEST AT 20 KT. IT
CONTINUES TO ALIGN WELL WITH A LARGE SURGE OF DEEP LAYER
MOISTURE WITH MAXIMUM VALUES NEAR THE LOW CENTER. THERE
CONTINUES TO BE DRY AIR AND DUST WRAPPING AROUND THE NORTHERN
EXTENT OF THE WAVE...WHICH MAY EXPLAIN THE LACK OF DEEP
CONVECTION NEAR THE CENTER. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS MAINLY S OF THE LOW CENTER FROM 11N-14N BETWEEN
43W-49W...AND FROM 14N-16N BETWEEN 48W-51W. IF CONVECTION
INCREASES NEAR THE LOW CENTER...THEN A TROPICAL DEPRESSION COULD
FORM.

TROPICAL WAVE EXTENDS FROM THE CAPE VERDE ISLANDS NEAR 18N23W TO
A 1010 MB SURFACE LOW NEAR 12N27W. THE LOW IS EMBEDDED WITHIN
THE MONSOON TROUGH...AN AN ASCAT PASS FROM EARLIER TODAY
INDICATES THAT THE LOW CENTER MAY ACTUALLY BE FARTHER SOUTH NEAR
10N. THE SYSTEM LIES ON THE WEST SIDE OF A SURGE OF DEEP LAYER
MOISTURE PRESENT IN TOTAL PRECIPITABLE WATER IMAGERY. IT ALSO
LIES WITHIN A CLEARING OF THE SAHARAN AIR LAYER THAT SURROUNDING
THE WAVE. A CLUSTER OF SCATTERED STRONG CONVECTION IS SW OF THE
LOW CENTER FROM 7N-11N BETWEEN 27W-31W. SOME GRADUAL DEVELOPMENT
OF THE SYSTEM IS POSSIBLE OVER THE NEXT COUPLE OF DAYS AS IT
MOVES W AT 15-20 KT.

A SURFACE TROUGH IN THE GULF OF MEXICO IS PRODUCING A LARGE AREA
OF SHOWERS/THUNDERSTORMS ACROSS THE BASIN. THE PORTION BEING
MONITORED FOR POSSIBLE DEVELOPMENT IS IN THE WESTERN GULF NEAR
THE COAST OF MEXICO. AN AIR FORCE RESERVE HURRICANE HUNTER
AIRCRAFT INVESTIGATED THE SYSTEM A FEW HOURS AGO AND FOUND AN
ELONGATED AREA OF LOW PRESSURE...BUT NOT A CLEAR LOW CENTER.
CONVECTION NEAR THIS PORTION OF THE TROUGH HAS ACTUALLY
DIMINISHED OVER THE PAST FEW HOURS. SCATTERED MODERATE
CONVECTION STILL REMAINS FROM 21N-24N BETWEEN 95W-98W...WITH
VERY DISORGANIZED SCATTERED MODERATE/ISOLATED STRONG CONVECTION
EXTENDING INLAND OVER MEXICO TO 103W. IF THE SYSTEM REMAINS OVER
WATER...SOME GRADUAL DEVELOPMENT IS POSSIBLE OVER THE NEXT
COUPLE OF DAYS.

...TROPICAL WAVES...

TWO TROPICAL WAVES IN THE CENTRAL AND EASTERN TROPICAL ATLC ARE
DESCRIBED IN THE SPECIAL FEATURES SECTION ABOVE.

TROPICAL WAVE IS ALONG 18N56W TO 10N56W MOVING W AT 15-20 KT.
THE WAVE ALIGNS WELL WITH A NARROW SURGE OF DEEP LAYER MOISTURE
PRESENT IN TOTAL PRECIPITABLE WATER IMAGERY. ONLY A SMALL AREA
OF ISOLATED MODERATE CONVECTION IS W OF THE AXIS FROM 16N-18N
BETWEEN 56W-59W.

WEAK TROPICAL WAVE IS MOVING THROUGH CENTRAL AMERICA AND THE
WESTERN CARIBBEAN FROM 20N85W TO 11N85W. THE WAVE IS MOVING WEST
AT 15-20 KT. IT LIES ON THE WEST SIDE OF A LARGE AREA OF
ENHANCED MOISTURE VALUES COVERING THE WESTERN HALF OF THE
CARIBBEAN. THE WAVE LIES BETWEEN AN UPPER LEVEL LOW TO THE WEST
AND AN UPPER LEVEL RIDGE TO THE EAST...WHICH MEANS THAT MOIST
SLY FLOW ALOFT IS OVER THE WAVE. CONVECTION IS CONCENTRATED
ALONG THE WAVE AXIS MAINLY OVER CENTRAL AMERICA INCLUDING
HONDURAS...NICARAGUA...AND COSTA RICA. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS ALSO OFFSHORE FROM
11N-14N BETWEEN 79W-84W WITH SIMILAR ACTIVITY ACROSS COSTA RICA
AND PANAMA. THIS ACTIVITY MAY BE MORE ASSOCIATED WITH DIFFLUENCE
ALOFT AND THE PRESENCE OF THE MONSOON TROUGH WHICH EXTENDS
THROUGH PANAMA TO NORTHERN COLOMBIA.

...THE ITCZ/THE MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS WEST AFRICA TO THE COAST OF
SENEGAL AT 13N17W TO A 1010 MB SURFACE LOW AT 12N28W WHERE IT
MAKES A U-SHAPE ALONG 8N31W TO 10N38W. THERE IS A BREAK IN THE
MONSOON TROUGH DUE TO THE LARGE CIRCULATION AROUND A 1009 MB
SURFACE LOW AT 16N47W. IT BEGINS AGAIN AT THIS LOW CENTER
CONTINUING ALONG 11N50W 10N54W TO 7N59W.

...DISCUSSION...

THE GULF OF MEXICO...
ACTIVE WEATHER IS ACROSS A LARGE PORTION OF THE GULF OF MEXICO
ASSOCIATED WITH A SURFACE TROUGH EXTENDING FROM THE FLORIDA
PANHANDLE AT 31N86W TO THE COAST OF MEXICO ALONG 27N91W TO
22N97W. A SWATH OF SHOWERS/THUNDERSTORMS EXTENDS 200 NM SE OF
THE AXIS. THE TROUGH IS SUPPORTED BY AN UPPER LEVEL TROUGH
EXTENDING FROM THE GREAT LAKES REGION TO THE EASTERN COAST OF
TEXAS. THE WESTERN EXTENT OF THE SURFACE TROUGH IS BEING
MONITORED FOR POSSIBLE DEVELOPMENT INTO A TROPICAL CYCLONE. SEE
SPECIAL FEATURES ABOVE FOR MORE DETAILS. ELSEWHERE ACROSS THE
BASIN...SURFACE RIDGING IS ACROSS THE SE GULF WITH 15-20 KT
SOUTHERLY FLOW PRESENT UNTIL HITTING THE WEAK NW FLOW ON THE
OPPOSITE SIDE OF THE SURFACE TROUGH. THIS CONVERGENCE IS HELPING
FORM THE LINE OF THUNDERSTORMS AHEAD OF THE TROUGH AXIS. BESIDES
NEAR THE SURFACE TROUGH...DRY AIR ALOFT IS OVER BOTH THE EXTREME
NW GULF AND THE SE GULF...WHICH IS PROVIDING MOSTLY FAIR
CONDITIONS. THE SURFACE TROUGH IS EXPECTED TO BREAK IN THE
MIDDLE WITH THE NE PORTION REMAINING MOSTLY STATIONARY AND
BRINGING SHOWERS/THUNDERSTORMS OVER THE NE GULF. THE WESTERN
PORTION IS EXPECTED TO TAKE ON A MORE VERTICAL
ORIENTATION...WITH POSSIBLE DEVELOPMENT AS MENTIONED ABOVE.

THE CARIBBEAN SEA...
A TROPICAL WAVE IS MOVING THROUGH THE WESTERN CARIBBEAN AND
CENTRAL AMERICA CAUSING SHOWERS/THUNDERSTORMS MAINLY OVER
CENTRAL AMERICA. SCATTERED SHOWER/THUNDERSTORMS ARE ALSO ACROSS
THE SW CARIBBEAN INCLUDING COSTA RICA AND PANAMA ASSOCIATED WITH
THE MONSOON TROUGH THAT EXTENDS THROUGH PANAMA TO A 1010 MB
SURFACE LOW OVER NORTHERN COLOMBIA. SHOWER ACTIVITY NEAR BOTH
THESE FEATURES IS ENHANCED BY DIFFLUENCE ALOFT BETWEEN AN UPPER
LEVEL LOW OVER BELIZE...AND AN UPPER LEVEL RIDGE CENTERED NEAR
14N79W. DRY AIR ALOFT COVERS THE REMAINDER OF THE CARIBBEAN
PROVIDING MOSTLY FAIR WEATHER. SEVERAL STATIONS ARE REPORTING
THE PRESENCE OF DUST...WHICH IS FURTHER SUPPORTING FAIR
CONDITIONS. A TROPICAL WAVE EAST OF THE LESSER ANTILLES WILL
LIKELY REACH THE EASTERN CARIBBEAN WITHIN THE NEXT 12 HOURS.
INTERESTS IN THE LESSER ANTILLES SHOULD ALSO MONITOR THE SYSTEM
TO THE EAST OF THIS WAVE THAT IS DESCRIBED IN THE SPECIAL
FEATURES SECTION. SHOWERS/THUNDERSTORMS WILL ALSO LIKELY REMAIN
ACROSS CENTRAL AMERICA AND THE SW CARIBBEAN.

THE ATLANTIC OCEAN...
SURFACE RIDGING DOMINATES THE WEST ATLC AROUND A 1021 MB HIGH
NEAR 28N61W PROVIDING MOSTLY FAIR CONDITIONS. HOWEVER...A STRONG
UPPER TROUGH OVER THE EASTERN CONUS IS PRODUCING STRONG
SHOWERS/THUNDERSTORMS ALONG THE EASTERN COAST OF FLORIDA AND THE
OFFSHORE WATERS N OF 26N BETWEEN 78W-81W. THE RIDGE IS SUPPORTED
BY A BROAD UPPER LEVEL RIDGE CENTERED TO THE N NEAR 35N60W. AN
UPPER LEVEL TROUGH IS TO THE SOUTH FROM NEAR 26N59W TO
20N75W...BUT IS INFILTRATED WITH DRY AIR WHICH IS LIMITING ITS
INFLUENCE TO PRODUCE ANY ACTIVE WEATHER. ONLY A SMALL AREA OF
SHOWERS IS FROM 26N-28N BETWEEN 59W-64W. THE REMAINDER OF THE
BASIN IS DOMINATED BY BROAD SURFACE RIDGING AROUND A 1019 MB
HIGH NEAR 26N35W. THE RIDGE IS SUPPORTED BY AN UPPER LEVEL RIDGE
CENTERED NEAR 21N50W. AN UPPER LEVEL TROUGH COVERS THE NE ATLC
SUPPORTING A WEAK SURFACE TROUGH ENTERING THE DISCUSSION AREA
ALONG 32N34W TO 29N41W. ISOLATED SHOWERS ARE WITHIN 90 NM EITHER
SIDE OF THE AXIS. VISIBLE SATELLITE IMAGERY AND SATELLITE
ENHANCED IMAGERY INDICATES A LARGE AREA OF SAHARAN DUST EXTENDS
FROM THE COAST OF AFRICA AROUND THE SERIES OF ATLC TROPICAL
WAVES TO THE EASTERN CARIBBEAN.

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

$$
WALTON





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