[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 231800
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU JUL 23 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 26W S OF 20N MOVING W NEAR 18 KT. THIS
WAVE COINCIDES WITH A DEEP MOISTURE MAXIMUM OBSERVED ON TOTAL
PRECIPITABLE WATER IMAGERY. SATELLITE IMAGERY ALSO INDICATES
LOW-LEVEL CYCLONIC FLOW IN THE VICINITY OF THE WAVE AXIS WITH A
LOW/MID-LEVEL DRY SAHARAN AIR LAYER SURROUNDING THE WAVE...WHICH
IS ACTING TO LIMIT DEEP CONVECTION. SCATTERED SHOWERS AND
ISOLATED MODERATE CONVECTION REMAINS MOSTLY WITHIN THE ITCZ AXIS
FROM 10N-14N BETWEEN 21W-30W.

A TROPICAL WAVE IS ALONG 61W S OF 19N MOVING W NEAR 25 KT. AFTER
ANALYZING THE UPPER AIR TIME SECTION ANALYSES FROM BARBADOS AND
GUADELOUPE...IT APPEARS THE WAVE AXIS PASSED BARBADOS AROUND
22/1800 UTC WHILE LOW-LEVEL WINDS REMAIN MOSTLY NELY AT
GUADELOUPE THROUGH 23/0600 UTC. VISIBLE SATELLITE IMAGERY
INDICATES THIS WAVE EXHIBITS AN INVERTED-V SIGNATURE IN THE
LOW-LEVEL CLOUD FIELD. THIS WAVE IS FOLLOWED BY A DRY
LOW/MID-LEVEL SAHARAN AIR LAYER. SCATTERED MODERATE CONVECTION
IS FROM 12N-15N BETWEEN 55W-62W.

A TROPICAL WAVE IS ALONG 73W S OF 20N MOVING W NEAR 20 KT. THIS
WAVE CONTINUES TO MOVE BENEATH NELY FLOW ALOFT WITH MODERATE TO
STRONG SUBSIDENCE DOMINATING ACROSS THE ERN AND CENTRAL
CARIBBEAN. ALSO A SAHARAN AIR LAYER OF DUST IS ACROSS MOST OF
THE CARIBBEAN BASIN HELPING TO KEEP ISOLATED SHOWERS LIMITED TO
S OF 13N BETWEEN 70W-75W AND MOST LIKELY RELATED MORE TO THE
PROXIMITY OF THE ITCZ AXIS ACROSS NRN VENEZUELA AND COLOMBIA.

A TROPICAL WAVE IS ALONG 89W S OF 20W MOVING W NEAR 23 KT. THIS
WAVE IS EMBEDDED WITHIN A BROAD AREA OF DEEP LAYER MOISTURE
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. MOST OF THE DEEP
CONVECTION ASSOCIATED WITH THIS WAVE IS IN THE E PACIFIC DUE TO
AN UPPER LEVEL RIDGE OVER THE NRN PORTION OF THE WAVE
ORIGINATING IN THE NW CARIBBEAN NEAR 18N84W. HOWEVER...SCATTERED
SHOWERS ARE OVER NRN CENTRAL AMERICA S OF 18W W OF 88W.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 11N15W 11N24W 11N27W 10N42W
12N59W. SCATTERED MODERATE CONVECTION IS FROM 5N-12N BETWEEN
15W-20W. ELSEWHERE...SCATTERED SHOWERS ARE PRIMARILY WITHIN 100
NM EITHER SIDE OF THE AXIS BETWEEN 27W-57W.

...DISCUSSION...

GULF OF MEXICO...
LOW-LEVEL CONVERGENCE ACROSS THE NRN GULF COAST IS FOCUSED ALONG
A STATIONARY BOUNDARY THAT IS DRAPED FROM SRN MISSISSIPPI
THROUGH SRN LOUISIANA AND INLAND 30/60 NM ALONG THE TEXAS GULF
COAST. A PRE-FRONTAL TROUGH IS ALSO ANALYZED FROM NEAR MOBILE
BAY INTO THE GULF NEAR 28N93W. THESE SURFACE FEATURES ALONG WITH
UPPER LEVEL DIFFLUENCE ALOFT CENTERED ON AN UPPER HIGH NEAR
27N93W ARE SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS OVER
THE FAR WRN FLORIDA PANHANDLE AND NRN GULF WATERS N OF 27N
BETWEEN 86W-93W. THE REMAINDER OF THE GULF IS UNDER A BROAD
SURFACE RIDGE ANCHORED BY A 1017 MB HIGH NEAR 28N84W BRINGING
GENERALLY FAIR WEATHER ACROSS THE FLORIDA PENINSULA...CENTRAL
AND SRN GULF S OF 27N. THE SURFACE RIDGE IS FORECAST TO SHIFT
EWD WHILE THE FRONTAL SYSTEM ACROSS SE TEXAS AND CENTRAL
LOUISIANA REMAINS MOSTLY ALONG OR JUST INLAND ALONG THE GULF
COAST AND DISSIPATES BY SATURDAY. INCREASING E TO SE FLOW WILL
DEVELOP ACROSS THE WRN GULF BY SUNDAY.

CARIBBEAN SEA...
A BROAD UPPER LEVEL HIGH IS OVER THE NW CARIBBEAN CENTERED NEAR
18N84W. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH THIS UPPER LEVEL
RIDGE IS GENERATING SCATTERED SHOWERS MAINLY ACROSS NRN PORTIONS
OF CENTRAL AMERICA N OF 15N W OF 84W. THE UPPER LEVEL RIDGING
CONTINUES NE ACROSS CENTRAL CUBA AND IS ENHANCING SCATTERED
SHOWERS AND ISOLATED TSTMS FROM 19N-22N BETWEEN 77W-81W. THE
NERN AND CENTRAL CARIBBEAN ARE EXPERIENCING GENERALLY FAIR
WEATHER DESPITE THE PRESENCE OF A TROPICAL WAVE ALONG 73W. DEEP
LAYER DRY AIR...AND SUBSIDENCE IN NELY FLOW ALOFT ARE INHIBITING
DEEP CONVECTION NEAR THE WAVE AND ACROSS THE CENTRAL CARIBBEAN.
HOWEVER ACROSS THE SE CARIBBEAN AND LESSER ANTILLES...SCATTERED
SHOWERS AND ISOLATED TSTMS WILL CONTINUE TO INCREASE IN COVERAGE
AS THE TROPICAL WAVE ALONG 61W IMPACTS THAT REGION OF THE BASIN.
FRESH TO STRONG ELY TRADE WINDS WILL PREVAIL ACROSS THE CENTRAL
CARIBBEAN THROUGH THE WEEKEND.

ATLANTIC OCEAN...
A SHORTWAVE UPPER LEVEL TROUGH IS N OF 25N W OF 73W ACROSS THE
FAR WRN PORTIONS OF THE SW NORTH ATLC AND SE CONUS. THIS UPPER
TROUGH IS SUPPORTING A SURFACE TROUGH EXTENDING FROM 28N74W TO
BEYOND 32N73W. LOW-LEVEL CONVERGENCE COUPLED WITH STRONG UPPER
LEVEL DIFFLUENCE E OF THE UPPER LEVEL TROUGH AXIS ALONG 73W IS
SUPPORTING SCATTERED SHOWERS AND TSTMS N OF 26N BETWEEN 69W-75W.
MORE WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS ARE FROM
23N-26N BETWEEN 67W-79W...INCLUDING THE BAHAMAS. FARTHER TO THE
E...MIDDLE TO UPPER LEVEL LIFT ASSOCIATED WITH A UPPER LOW
CENTERED NEAR 28N56W IS GENERATING ISOLATED SHOWERS FROM 23N-33N
BETWEEN 50W-62W. THE REMAINDER OF THE CENTRAL AND E ATLC IS
DOMINATED BY A 1025 MB SURFACE HIGH CENTERED N OF THE DISCUSSION
AREA NEAR 37N48W RESULTING IN GENERALLY FAIR WEATHER. HOWEVER...
A STATIONARY FRONT IS POSITIONED FROM SERN SPAIN THROUGH THE
MADEIRA ISLANDS TO 30N25W WITH LINGERING ISOLATED SHOWERS WITHIN
60 NM S OF THE FRONT.

$$
HUFFMAN




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