[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 181758
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT JUL 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 31W S OF 19N MOVING W NEAR 15 KT.
ALTHOUGH THE WAVE LACKS ANY SIGNIFICANT DEEP CONVECTION DUE TO
THE PRESENCE OF SAHARAN DUST TO THE NORTH AND EAST OF THE WAVE
AXIS...SLIGHT LOW TO MIDDLE LEVEL CYCLONIC TURNING OF THE CLOUD
FIELD IS NOTED IN THE SATELLITE CLOUD DRIFT WINDS WITH THIS WAVE.

A TROPICAL WAVE IS ALONG 44W S OF 16N MOVING W NEAR 20 KT. THIS
WAVE COINCIDES WITH A LOW TO MIDDLE LEVEL CYCLONIC CIRCULATION
ALONG THE WAVE AXIS NEAR 12N. SCATTERED MODERATE CONVECTION IS
FROM 10N-14N BETWEEN 43W-47W.

A TROPICAL WAVE EXTENDS ALONG 21N58W 15N61W TO 10N62W MOVING
W NEAR 18 KT. THIS WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER
MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM
CIMSS. WATER VAPOR IMAGERY INDICATES THE WAVE IS BEGINNING TO
MOVE BENEATH AN UPPER LEVEL RIDGE ACROSS THE ERN CARIBBEAN AND
THE NRN PORTION OF THE WAVE IS COMING UNDER THE IMPACTS OF AN
UPPER LOW CENTERED NE OF PUERTO RICO NEAR 23N58W. UPPER LEVEL
DIFFLUENCE BETWEEN THESE TWO FEATURES ARE ENHANCING SCATTERED
MODERATE CONVECTION FROM 13N-18N BETWEEN 55W-62W.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 10N14W 9N29W 10N34W 11N42W 8N46W
13N60W. SCATTERED MODERATE CONVECTION IS WITHIN 120 NM OF A LINE
FROM 10N12W TO 6N24W. SIMILAR CONVECTION IS FROM 6N-9N BETWEEN
47W-52W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL RIDGE IS PRESENT ACROSS THE NRN FLORIDA PENINSULA
AND THE NRN GULF N OF 25N...WITH A SURFACE RIDGE ACROSS THE
CENTRAL GULF AND SRN GULF ANCHORED ON A 1020 MB HIGH NEAR
26N83W. STABLE ATMOSPHERIC CONDITIONS AND SUBSIDENCE ASSOCIATED
WITH THE SURFACE HIGH AND SURFACE RIDGE ARE RESULTING IN
GENERALLY FAIR WEATHER ACROSS THE SRN GULF S OF 25N. HOWEVER...
ACROSS THE NRN GULF COAST AND NRN FLORIDA...UPPER LEVEL MOISTURE
IS INTERACTING WITH ATMOSPHERIC LIFT ASSOCIATED WITH AN UPPER
LEVEL TROUGH PROGRESSING ACROSS THE SE CONUS THAT IS SUPPORTING
A COLD FRONT OVER SRN GEORGIA...THE FLORIDA PANHANDLE AND THE
GULF COAST TO NEAR NEW ORLEANS LOUISIANA. A PRE-FRONTAL TROUGH
IS ALSO ANALYZED FROM PANAMA CITY FLORIDA W-SW TO 29N94W.
DOPPLER RADAR AND LIGHTNING DATA INDICATES SCATTERED SHOWERS AND
TSTMS ARE OCCURRING N OF 26N BETWEEN 81W-96W. ANTICYCLONIC FLOW
AROUND THE SURFACE RIDGE IS SUPPORTING GENERALLY E TO SE WINDS
OF 10-15 KT ACROSS A MAJORITY OF THE SRN GULF.

CARIBBEAN SEA...
FRESH TO STRONG TRADE WINDS ARE OCCURRING BETWEEN THE
SUBTROPICAL RIDGE OVER THE CENTRAL ATLC AND A BROAD TROUGH OVER
NWRN SOUTH AMERICA...WITH THE STRONGEST FLOW NEAR THE COAST OF
COLOMBIA. AN EARLIER SCATTEROMETER PASS AROUND 1100 UTC DEPICTED
A LARGE AREA OF NE TO E WINDS OF 20 TO 30 KT ACROSS THE CENTRAL
AND SW CARIBBEAN. THESE TRADE WINDS ARE FORECAST TO REMAIN FRESH
TO STRONG THROUGH MONDAY AS THE SUBTROPICAL RIDGE REMAINS IN
PLACE. HOWEVER...THIS SURFACE WIND REGIME WILL FLUCTUATE WITH
THE APPROACH OF THE TROPICAL WAVE BEGINNING TO IMPACT THE LESSER
ANTILLES THIS AFTERNOON AND EVENING. SCATTERED SHOWERS AND TSTMS
ARE CONCENTRATED MAINLY E OF 64W AND ARE BEING ENHANCED BY AN
UPPER LEVEL DIFFLUENT PATTERN DUE TO AN UPPER HIGH CENTERED NEAR
14N66W. IN THE FAR SW CARIBBEAN AND ACROSS WRN PANAMA...COSTA
RICA AND ERN NICARAGUA...SCATTERED SHOWERS AND TSTMS ARE S OF A
LINE FROM 9N80W TO 14N83W AND ALSO THE RESULT OF DIVERGENT FLOW
ALOFT.

ATLANTIC OCEAN...
DEEP LAYER MOISTURE IS COMBINING WITH UPPER LEVEL DIFFLUENCE E
OF AN UPPER LEVEL TROUGH ACROSS THE SE CONUS TO RESULT IN
SCATTERED SHOWERS AND TSTMS ACROSS NRN FLORIDA AND A PORTION OF
THE SW NORTH ATLC WATERS FROM 28N-32N BETWEEN 74W-78W. ELSEWHERE
ACROSS THE SW NORTH ATLC...SUBSIDENCE AND GENERALLY FAIR WEATHER
ARE PRESENT AS A SURGE RIDGE OF HIGH PRESSURE EXTENDS FROM THE
BAHAMAS NEWD TO BEYOND 32N50W. THE CENTRAL ATLC WATERS ARE BEING
INFLUENCED BY THE NRN EXTENT OF A TROPICAL WAVE S OF 21N ALONG
APPROXIMATELY 60W WITH AN UPPER LEVEL LOW CENTERED NEAR 23N58W
THAT IS ENHANCING SCATTERED SHOWERS AND TSTMS FROM 13N-18N
BETWEEN 55W-62W. ALSO...UPPER DIFFLUENCE E OF THE UPPER TROUGH
IS GENERATING POSSIBLE SCATTERED SHOWERS FROM 18N-25N BETWEEN
48W-56W. ELSEWHERE ACROSS THE CENTRAL AND E ATLC...A BROAD
SURFACE RIDGE ASSOCIATED WITH A 1034 MB HIGH IS CENTERED NEAR
THE AZORES. ACROSS THE TROPICAL ATLC...AN UPPER LEVEL RIDGE
EXTENDS FROM THE CAPE VERDE ISLANDS NEAR 16N25W TO AN UPPER
LEVEL HIGH NEAR 17N47W TO 14N54W. UPPER LEVEL DIVERGENCE
ASSOCIATED WITH THE UPPER LEVEL RIDGE IS SUPPORTING THE
CONVECTION ALONG THE ITCZ AND IN THE VICINITY OF THE TROPICAL
WAVE IMPACTING THE LESSER ANTILLES.

$$
HUFFMAN


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