[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 180531
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0445 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 33W/34W S OF 13N MOVING W 15-20 KT. THE
WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN
TOTAL PRECIPITABLE WATER IMAGERY. QUIKSCAT IMAGERY FROM LAST
NIGHT ALONG WITH ASCAT DATA FROM A 0016 UTC PASS INDICATE BROAD
LOW-LEVEL CYCLONIC TURNING IN THE VICINITY OF THE WAVE AXIS.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 6N-15N
BETWEEN 30W-35W. IT IS HARD TO DETERMINE IF THIS ACTIVITY IS
ASSOCIATED MORE WITH THE WAVE OR THE ITCZ.

TROPICAL WAVE IS ADDED ON THE 18/0000 UTC ANALYSIS ALONG 53W S
OF 13N MOVING W 15-20 KT. THIS WAVE HAS PREVIOUSLY BEEN ANALYZED
AS A SURFACE TROUGH EMBEDDED WITHIN THE ITCZ. HOWEVER...BASED ON
CONTINUOUS WWD PROPAGATION AND A 2206 UTC QUIKSCAT PASS
CONFIRMING LOW-LEVEL CYCLONIC FLOW ABOUT THE AXIS...THE TROUGH
IS NOW ANALYZED AS A WAVE. THE WAVE ALSO COINCIDES WITH A DEEP
LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER
IMAGERY. ISOLATED MODERATE CONVECTION IS WITHIN 150 NM OF THE
AXIS FROM 9N-10N.

TROPICAL WAVE PREVIOUSLY ALONG 79W HAS BE RELOCATED ALONG 76W S
OF 17N MOVING W 15-20 KT. THE RELOCATION WAS BASED ON A STRONGER
DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER
IMAGERY THAT AN BE TRACED BACK ACROSS THE TROPICAL ATLC. WHILE
THERE STILL IS MOISTURE AND CYCLONIC FLOW NEAR THE PREVIOUS WAVE
LOCATION...TRACING BACK THE ORIGINS OF THAT FEATURE INDICATE A
NON-TROPICAL ORIGINATION. HENCE...THE NON-TROPICAL FEATURE IS
NOW ANALYZED AS A SURFACE TROUGH. THE NEW WAVE POSITION IS UNDER
A DIFFLUENT ZONE ALOFT ENHANCING CONVECTION NEAR THE WAVE.
SCATTERED STRONG CONVECTION IS OVER COLOMBIA FROM 5N-10N
BETWEEN 74W-78W...AND FROM 17N-22N BETWEEN 73W-79W.

...THE ITCZ...

ITCZ AXIS IS CENTERED ALONG 13N17W 9N25W 8N33W 7N44W 7N60W.
SCATTERED STRONG CONVECTION IS FROM 10N-15N BETWEEN 17W-25W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 150 NM S
OF THE AXIS...AND WITHIN 50 NM N OF THE AXIS BETWEEN 20W-30W.
SIMILAR ACTIVITY IS ALONG ALONG A LINE FROM 10N48W TO 13N42W.


...DISCUSSION...

THE GULF OF MEXICO...
AS OF 0300 UTC...THE TAIL END OF A COLD FRONT REMAINS ACROSS THE
YUCATAN PENINSULA AND SW GULF ALONG 20N88W 20N92W 18N94W. THE
REST OF THE COLD FRONT HAS NOW PUSHED SE OUT OF THE BASIN. A FEW
ISOLATED SHOWERS/POSSIBLE THUNDERSTORMS ARE IN THE BAY OF
CAMPECHE NEAR 19N93W IN ASSOCIATION WITH THE FRONT. THE FRONT IS
SUPPORTED BY AN UPPER LEVEL TROUGH OVER THE ERN CONUS AND WRN
ATLC THAT DIPS ACROSS THE GULF OF MEXICO N OF 21N. A SMALL
PORTION OF AN UPPER LEVEL RIDGE COVERS THE FAR SW BASIN
EXTENDING FROM MEXICO. BEHIND THE FRONT...STRONG HIGH PRESSURE
IS BUILDING SUPPORTED BY STRONG SUBSIDENCE ALOFT N OF 26N.
SURFACE WINDS OF 20 TO 25 KT REMAIN ACROSS MUCH OF THE BASIN
REACHING 30 KT IN SOME PORTIONS.

THE CARIBBEAN SEA...
AS OF 0300 UTC...A COLD FRONT PREVIOUSLY OVER THE GULF OF MEXICO
HAS PUSHED INTO THE FAR NW CARIBBEAN ACROSS CUBA TO THE YUCATAN
PENINSULA FROM 23N80W TO 20N88W. ISOLATED SHOWERS/THUNDERSTORMS
ARE WITHIN 100 NM OF THE FRONT. A SURFACE TROUGH EXTENDS FROM
19N83W TO 13N84W. THIS TROUGH WAS PREVIOUSLY ANALYZED AS A
TROPICAL WAVE. HOWEVER...TRACING BACK THE ORIGIN OF THE FEATURE
IT APPEARS THAT IT IS NOT OF TROPICAL DECENT. HENCE...IT IS NOW
ANALYZED AS A SURFACE TROUGH. SEE THE TROPICAL WAVE SECTION FOR
MORE DETAILS ON THIS FEATURE AND THE TROPICAL WAVE ALONG 76W.
SURFACE CONVERGENCE NEAR BOTH OF THESE FEATURES...AS WELL AS
DIFFLUENT FLOW ALOFT AROUND AN UPPER LEVEL TROUGH COVERING THE
BASIN CENTERED OVER COLOMBIA NEAR 11N74W ARE SUPPORTING A LARGE
AREA OF SCATTERED SHOWERS/THUNDERSTORMS EXTENDING FROM NICARAGUA
TO WRN CUBA AND HISPANIOLA FROM 14N-21N BETWEEN 73W-82W. IT IS
HARD TO DETERMINE WHICH FEATURE IS INFLUENCING THIS ACTIVITY THE
MOST. ISOLATED SHOWERS/THUNDERSTORMS ARE ALSO S OF 14N W OF 77W.
THE ERN CARIBBEAN REMAINS FAIRLY CALM E OF 73W. EXPECT THE COLD
FRONT IN THE FAR NW CARIBBEAN TO CONTINUE PUSHING SE AND MERGE
WITH THE SURFACE TROUGH ALONG 83W/84W. THE TROPICAL WAVE ALONG
76W WILL CONTINUE PROPAGATING WWD.

THE ATLANTIC OCEAN...
AS OF 0300 UTC...A COLD FRONT ENTERS THE DISCUSSION AREA FROM A
1007 MB SURFACE LOW NEAR 32N75W EXTENDING ALONG 30N74W 26N77W TO
ERN CUBA NEAR 23N80W. RECENT LIGHTNING DATA INDICATES NUMEROUS
SHOWERS/THUNDERSTORMS WITHIN 30 NM OF THE FRONT AXIS. ISOLATED
SHOWERS/THUNDERSTORMS ARE ALSO OUT AHEAD OF THE FRONT N OF 24N
BETWEEN 67W-72W. THE FRONT IS SUPPORTED BY AN UPPER LEVEL TROUGH
OVER THE ERN CONUS EXTENDING INTO THE WRN ATLC. SCATTERED
SHOWERS/THUNDERSTORMS ARE BETWEEN THE WRN BAHAMAS AND CUBA S OF
23N BETWEEN 74W-77W DUE TO UPPER LEVEL DIFFLUENCE BETWEEN AN
UPPER LEVEL TROUGH COVERING THE CARIBBEAN AND AN UPPER LEVEL
RIDGE OVER THE REMAINDER OF THE WRN ATLC CENTERED NEAR 31N53W.
THE UPPER LEVEL RIDGE IS SUPPORTING A BROAD SURFACE RIDGE OVER
THE WRN ATLC ANCHORED BY A 1022 MB SURFACE HIGH NEAR 33N49W.
FARTHER E...A SURFACE TROUGH ENTERS THE DISCUSSION AREA NEAR
32N36W EXTENDING TO 19N45W. 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
30N26W TO 19N32W. NO SHOWER ACTIVITY IS CURRENTLY ASSOCIATED
WITH THE TROUGH. THIS TROUGH IS ALSO SUPPORTED BY THE UPPER
LEVEL LOW. THE REMAINDER OF THE BASIN IS DOMINATED BY A BROAD
UPPER LEVEL RIDGE S OF 21N 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 16N32W TO 24N16W.

$$
WALTON



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