[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 282353
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI AUG 28 2009

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

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2230 UTC.

...SPECIAL FEATURES...

TROPICAL STORM DANNY IS CENTERED NEAR 30.9N 75.1W OR ABOUT 300
MILES...480 KM...SOUTH OF CAPE HATTERAS NORTH CAROLINA AND ABOUT
765 MILES...1230 KM...SOUTH-SOUTHWEST OF NANTUCKET MASSACHUSETTS
AT 29/0000 UTC. DANNY IS MOVING TO THE NNE AT 7 KT. THE MINIMUM
CENTRAL PRESSURE IS 1006 MB. MAXIMUM SUSTAINED WIND SPEED IS 35
KT WITH GUSTS TO 45 KT. SOME SLIGHT STRENGTHENING IS POSSIBLE
TONIGHT...WITH LITTLE CHANGE IN INTENSITY EXPECTED ON SATURDAY.
DANNY IS EXPECTED TO BECOME EXTRATROPICAL ON SATURDAY NIGHT. SEE
LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS
MIATCPAT5/WTNT35 KNHC AND THE FULL FORECAST/ ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT5/WTNT25 KNHC FOR MORE DETAILS. THE
LOW LEVEL CENTER IS COMPLETELY EXPOSED AS THE DEEP CONVECTION IS
TO THE E. SCATTERED MODERATE/STRONG CONVECTION IS FROM 26N-32N
BETWEEN 70W-75W.

A STRONG TROPICAL WAVE IS ALONG 37W/38W S OF 17N MOVING W NEAR
20 KT. A 1011 MB LOW IS ALONG THE WAVE AXIS NEAR 10N. VISIBLE
SATELLITE IMAGERY AND SATELLITE DERIVED WINDS INDICATE BROAD
LOW-LEVEL CYCLONIC FLOW IN THE VICINITY OF THE WAVE AXIS
CONCENTRATED AROUND THE SURFACE LOW CENTER. THE WAVE/LOW ALSO
COINCIDE WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL
PRECIPITABLE WATER IMAGERY. CONDITIONS APPEAR FAVORABLE FOR SLOW
DEVELOPMENT OF THIS SYSTEM OVER THE NEXT COUPLE OF DAYS. THERE
IS A MEDIUM CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM BECOMING
A TROPICAL CYCLONE DURING THE NEXT 48 HRS. SCATTERED
MODERATE/STRONG CONVECTION IS FROM 7N-13N BETWEEN 38W-44W.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 55W S OF 15N MOVING W 15-20 KT. THE
WAVE COINCIDES WITH A PEAK IN MOISTURE OBSERVED IN TOTAL
PRECIPITABLE WATER IMAGERY. HOWEVER...DUE TO DRY LOWER
LEVELS...NO DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH THE
WAVE.

A TROPICAL WAVE IS ALONG 85W S OF 16N MOVING W NEAR 18 KT. THE
WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM IN THE E
PACIFIC OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. THE WAVE
RECENTLY MOVED UNDER AN UPPER LEVEL DIFFLUENT ZONE WHICH IS
ENHANCING CONVECTION OVER CENTRAL AMERICA WITH 75 NM EITHER SIDE
OF THE WAVE AXIS INCLUDING PORTIONS OF NICARAGUA AND COSTA RICA.
MORE DEEP CONVECTION IS NOTED IN THE E PACIFIC ALONG THE WAVE
AXIS. SEE THE TWDEP FOR MORE DETAILS.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 14N17W 11N27W 8N40W 9N48W 11N57W
10N68W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM
14N-17N BETWEEN 16W-18W. SIMILAR CONVECTION IS FROM 10N-13N
BETWEEN 22W-26W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 2100 UTC...A SURFACE TROUGH EXTENDS ACROSS THE FLORIDA
PENINSULA INTO THE CENTRAL GULF OF MEXICO WITH AXIS ALONG 31N81W
27N82W 25N85W 24N88W. SCATTERED SHOWERS/THUNDERSTORMS ARE WITHIN
50 NM OF THE TROUGH AXIS. THE SURFACE TROUGH IS SUPPORTED BY A
SHORTWAVE UPPER LEVEL TROUGH EXTENDING ACROSS GEORGIA INTO THE
NE GULF TO NEAR 26N85W. THE SHORT WAVE UPPER TROUGH IS CONNECTED
TO A LARGER UPPER LEVEL TROUGH ACROSS THE CENTRAL UNITED STATES.
AS OF 2100 UTC...A WEAK 1014 MB SURFACE HIGH IS LOCATED OVER THE
NW GULF CENTERED NEAR 26N93W. AN UPPER LEVEL RIDGE CENTERED OVER
MEXICO NEAR 17N96W DOMINATES THE MAJORITY OF THE SRN GULF OF
MEXICO. UPPER LEVEL DIFFLUENCE BETWEEN THIS UPPER RIDGE AND THE
UPPER LEVEL TROUGH OVER THE CENTRAL UNITED STATES IS SUPPORTING
ISOLATED SHOWERS ACROSS THE NW GULF OF MEXICO FROM 24N-27N
BETWEEN 90W-94W. WINDS REMAIN LIGHT TO GENTLE ACROSS THE BASIN
BECOMING MODERATE NEAR THE YUCATAN PENINSULA. EXPECT THE SURFACE
RIDGE TO BUILD OVER THE NEXT DAY BEFORE A COLD FRONT ENTERS THE
NRN GULF SUN NIGHT.

CARIBBEAN SEA...
AN UPPER LEVEL LOW CENTERED NEAR 16N80W DOMINATES THE W
CARIBBEAN TO THE YUCATAN PENINSULA. UPPER LEVEL DIFFLUENCE
BETWEEN THIS LOW AND THE UPPER LEVEL RIDGE OVER THE GULF IS
SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE YUCATAN
PENINSULA AND ADJACENT COASTAL WATERS S OF 22N W OF 86W. UPPER
LEVEL DIFFLUENCE BETWEEN THE UPPER LOW AND A SHORTWAVE UPPER
LEVEL TROUGH OVER THE NE GULF IS ENHANCING NUMEROUS
SHOWERS/THUNDERSTORMS ACROSS THE CAYMAN ISLANDS AND CUBA.
SURFACE CONVERGENCE NEAR THE E PACIFIC ITCZ IS GENERATING
SCATTERED SHOWERS/THUNDERSTORMS IN THE SW CARIBBEAN S OF 11N W
OF 79W. A FEW ISOLATED SHOWERS ARE IN THE CENTRAL CARIBBEAN FROM
12N-19N BETWEEN 75W-78W DUE TO UPPER LEVEL DIFFLUENCE BETWEEN
THE UPPER LEVEL LOW OVER THE W CARIBBEAN AND AN UPPER LEVEL
RIDGE DOMINATING THE E CARIBBEAN. MODERATE TO FRESH TRADE WINDS
ARE OVER MUCH OF THE BASIN. EXPECT A TROPICAL WAVE CURRENTLY
ALONG 55W TO REACH THE LESSER ANTILLES TOMORROW NIGHT.

ATLANTIC OCEAN...
TROPICAL STORM DANNY REMAINS THE MAIN FOCUS ACROSS THE W ATLC.
A CLUSTER OF STRONG SHOWERS/THUNDERSTORMS ARE ACROSS THE FLORIDA
COAST FROM 26N-29N W OF 79W. ISOLATED SHOWERS ARE N OF 29N W OF
80W. BOTH AREAS OF SHOWER ACTIVITY ARE SUPPORTED BY SURFACE
CONVERGENCE AHEAD OF A SURFACE TROUGH EXTENDING ACROSS THE
FLORIDA PENINSULA FROM 31N81W TO 27N82W AND INTO THE GULF OF
MEXICO. THE ACTIVITY IS ALSO ENHANCED BY UPPER LEVEL DIFFLUENCE
BETWEEN A SHORTWAVE UPPER LEVEL TROUGH OVER GEORGIA AND THE NE
GULF OF MEXICO AND A BROAD UPPER LEVEL RIDGE OVER THE W ATLC
CENTERED NEAR 23N67W. ELSEWHERE ACROSS THE ATLC...A BROAD
SURFACE RIDGE DOMINATES ANCHORED BY A 1024 MB HIGH NEAR
33N59W...AND A STRONGER 1034 MB AZORES HIGH CENTERED NEAR 43N21W
BRINGING GENERALLY FAIR WEATHER ACROSS THE REMAINDER OF THE
BASIN. IN THE UPPER LEVELS...AN UPPER LEVEL LOW IS CENTERED NEAR
29N45W E OF THE AFOREMENTIONED UPPER RIDGE. A SECOND UPPER LEVEL
LOW IS OFF THE COAST OF AFRICA NEAR 26N22W. BETWEEN THESE TWO
UPPER LOWS...A BROAD UPPER LEVEL RIDGE CENTERED NEAR 17N38W
DOMINATES THE TROPICAL ATLC ENHANCING CONVECTION ALONG THE ITCZ.

$$
WALTON





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