[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 181045
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SUN OCT 18 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1000 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 35W S OF 14N MOVING W 15-20 KT. THE
WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN
TOTAL PRECIPITABLE WATER IMAGERY. THE FIRST VISIBLE SATELLITE
IMAGES OF THE DAY INDICATE CYCLONIC FLOW IN THE VICINITY OF THE
WAVE AXIS. SCATTERED MODERATE CONVECTION IS FROM 7N-10N BETWEEN
33W-37W...AND FROM 13N-16N BETWEEN 32W-36W.

TROPICAL WAVE IS ALONG 54W/55W S OF 12N MOVING W 15-20 KT.
SATELLITE IMAGERY INDICATES BROAD LOW-LEVEL CYCLONIC FLOW ABOUT
THE WAVE AXIS. THE WAVE ALSO COINCIDES WITH A LOW-AMPLITUDE DEEP
LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER
IMAGERY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM
7N-9N BETWEEN 55W-58W.

TROPICAL WAVE IS ALONG 78W S OF 17N MOVING W 15-20 KT. THE WAVE
LIES WITHIN A BROAD AREA OF DEEP MOISTURE OVER THE WRN CARIBBEAN
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY...AS WELL AS BROAD
LOW LEVEL CYCLONIC FLOW INDICATED IN SATELLITE IMAGERY. AN UPPER
LEVEL TROUGH COVERING THE CARIBBEAN IS PROVIDING A DIFFLUENT
ZONE ALOFT SUPPORTING A LARGE AREA OF CONVECTION OVER THE WRN
CARIBBEAN. SCATTERED MODERATE/STRONG CONVECTION IS FROM 3N-11N
BETWEEN 73W-80W...FROM 11N-17N BETWEEN 78W-83W...AND FROM
17N-20N BETWEEN 73W-78W. THIS CONVECTION IS PROBABLY MOST
INFLUENCED BY THE DIFFLUENCE ALOFT THAN SURFACE CONVERGENCE NEAR
THE WAVE.

...THE ITCZ...

ITCZ AXIS IS CENTERED ALONG 14N17W 9N24W 8N34W 7N44W 7N61W.
NUMEROUS STRONG CONVECTION IS FROM 12N-16N BETWEEN 17W-23W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 5N-7N
BETWEEN 11W-16W...FROM 6N-9N BETWEEN 19W-21W...FROM 11N-14N
BETWEEN 24W-27W...AND FROM 6N-11N BETWEEN 26W-32W.

...DISCUSSION...

THE GULF OF MEXICO...
THE COLD FRONT PREVIOUSLY IN THE GULF OF MEXICO HAS NOW PUSHED
COMPLETELY SE OUT OF THE BASIN. HIGH PRESSURE AND PARTLY CLOUDY
SKIES REMAIN IN THE WAKE OF THE FRONT. AN UPPER LEVEL TROUGH
OVER THE ERN CONUS EXTENDS OVER THE GULF N OF 21N. A SMALL
PORTION OF AN UPPER LEVEL RIDGE COVERS THE FAR SW BASIN
EXTENDING FROM MEXICO. STRONG SUBSIDENCE ALOFT CONTINUES TO
BUILD N OF 25N. SURFACE WINDS OF 20 TO 25 KT REMAIN ACROSS MUCH
OF THE BASIN...AND ARE FORECAST TO DIMINISH AS THE SURFACE HIGH
PRESSURE OVER THE BASIN BEGINS TO WEAKEN AND SHIFT E LATER TODAY.

THE CARIBBEAN SEA...
AS OF 0900 UTC...A COLD FRONT EXTENDS FROM CENTRAL CUBA NEAR
22N79W ALONG 20N84W 19N86W TO HONDURAS NEAR 16N88W. ISOLATED
SHOWERS/THUNDERSTORMS ARE WITHIN 75 NM OF THE FRONT. N TO NE
SURFACE WINDS OF 20-25 KT ARE NW OF THE FRONT. A TROPICAL WAVE
IS ALONG 78W. SURFACE CONVERGENCE NEAR THE WAVE ALONG WITH UPPER
LEVEL DIFFLUENCE AROUND AN UPPER TROUGH COVERING THE BASIN
CENTERED NEAR 11N75W ARE SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS FROM 3N-11N BETWEEN 73W-80W...FROM 11N-17N
BETWEEN 78W-83W...AND FROM 17N-20N BETWEEN 73W-78W. THE ACTIVITY
IS PROBABLY ENHANCED MORE BY THE UPPER LEVEL DIFFLUENCE THAN
SURFACE CONVERGENCE NEAR THE WAVE. THE ERN CARIBBEAN REMAINS
FAIRLY CALM E OF 73W WITH FRESH TO STRONG TRADEWINDS BETWEEN
68W-75W. EXPECT THE COLD FRONT IN THE FAR NW CARIBBEAN TO
CONTINUE PUSHING SE AND STALL AS IT BEGINS TO INTERACT WITH THE
TROPICAL WAVE ALONG 78W.

THE ATLANTIC OCEAN...
AS OF 0900 UTC...A COLD FRONT ENTERS THE DISCUSSION AREA NEAR
32N72W EXTENDING ALONG 27N75W TO CENTRAL CUBA NEAR 22N79W.
RECENT LIGHTNING DATA INDICATES SCATTERED SHOWERS/THUNDERSTORMS
WITHIN 75 NM OF THE FRONT AXIS. A FEW ISOLATED
SHOWERS/THUNDERSTORMS ARE ALSO OUT AHEAD OF THE FRONT FROM
27N-30N BETWEEN 66W-69W. THE FRONT IS SUPPORTED BY AN UPPER
LEVEL TROUGH OVER THE ERN CONUS EXTENDING INTO THE WRN ATLC. THE
REMAINDER OF THE WRN ATLC IS COVERED BY AN UPPER LEVEL RIDGE
CENTERED NEAR 30N57W. THE UPPER LEVEL RIDGE IS SUPPORTING A
BROAD SURFACE RIDGE OVER THE WRN ATLC ANCHORED BY A 1020 MB
SURFACE HIGH NEAR 30N57W...AND A 1023 MB HIGH NEAR 34N50W.
FARTHER E...A SURFACE TROUGH ENTERS THE DISCUSSION AREA NEAR
32N39W EXTENDING ALONG 26N39W TO 17N49W. ISOLATED SHOWERS ARE
ALONG THE TROUGH AXIS. THE TROUGH IS SUPPORTED BY AN UPPER LEVEL
LOW CENTERED NEAR 27N34W. A SECOND SURFACE TROUGH EXTENDS FROM A
WEAK 1015 MB SURFACE LOW NEAR 31N27W TO 21N34W. POSSIBLE
ISOLATED SHOWERS ARE WITHIN 100 NM OF THE THE AXIS. THIS TROUGH
IS ALSO SUPPORTED BY THE UPPER LEVEL LOW NEAR 27N34W. THE
REMAINDER OF THE BASIN IS DOMINATED BY A BROAD UPPER LEVEL RIDGE
S OF 22N E OF 40W. THIS UPPER RIDGE IS ENHANCING CONVECTION
ALONG THE ITCZ...AND ALSO SHEARING MOISTURE FROM THE ITCZ TO THE
NE. THIS MOISTURE IS SUPPORTING CLOUDS AND POSSIBLE ISOLATED
SHOWERS SE OF A LINE FROM 11N47W TO 23N16W.

$$
WALTON




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