[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 171803
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT FRI APR 17 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 1745 UTC.

...THE ITCZ...
THE ATLC ITCZ EXTENDS FROM THE AFRICAN COAST AT 06N09W TO ALONG
THE EQUATOR FROM 22W TO S AMERICA AT 49W. SCATTERED SHOWERS AND
TSTMS ARE OBSERVED WITHIN 120 NM EITHER SIDE OF LINE FROM 01S06W
TO 04N14W AND WITHIN 60 NM OF THE ITCZ AXIS W OF 15W.

...DISCUSSION...

THE GULF OF MEXICO...
THE UPPER LEVEL FLOW HAS BECOME ZONAL...W TO E...OVER THE GULF.
A MID LEVEL ANTICYCLONE IS NOTED NEAR 26N91W. REMNANTS OF A
FRONTAL TROUGH ARE CLEARLY EVIDENT FROM NW CUBA TO NE TEXAS WITH
THE PORTION OVER THE CENTRAL GULF MOVING NE AND ANALYZED AS A
WARM FRONT. MID LEVEL DIFFLUENCE OVER THE E SEMICIRCLE OF THE
MOSTLY MID LEVEL ANTICYCLONE ENHANCED CLUSTERS OF TSTMS NEAR
28N92W AND NEAR 25.5N27.5W EARLIER THIS MORNING...BUT THE
CONVECTION IS CURRENTLY DECREASING IN BOTH INTENSITY AND AREAL
COVERAGE. THE RESULTANT DEBRIS MOISTURE IS NOW ADVECTED E IN THE
UPPER FLOW OVER THE GULF N OF 25N E OF 90W...CONTINUING ACROSS
THE ENTIRE STATE OF FLORIDA AND THE NW BAHAMAS. ELSEWHERE AT THE
SURFACE A WEAK LOW PRES IS NOTED NEAR 21N97W WITH WEAK SHOWERS
WITHIN 120 NM OF CENTER. UPPER DRY AIR AND SUBSIDENCE IS
SUPPRESSING CONVECTION ELSEWHERE ACROSS THE GULF OF MEXICO.

UPSTREAM OVER CENTRAL TEXAS...AN UPPER SHORT WAVE IS SWINGING E
AND ENHANCING IMPRESSIVE CONVECTION. SOME OF THE DEBRIS MOISTURE
MAY SPREAD E OVER THE NW GULF OF MEXICO LATER TODAY WITH THE
ASSOCIATED SURFACE COLD FRONT MOVING OFF THE TEXAS COAST SAT.

THE CARIBBEAN SEA...
AN UPPER TROUGH EXTENDS S OVER THE N CENTRAL CARIBBEAN ACROSS
HISPANIOLA TO A BASE NEAR 12N82W...AND IS PROGRESSING EASTWARD
WITH TIME. IN THE WAKE OF THE TROUGH A MID LEVEL RIDGE HAS BUILT
SE FROM THE CENTRAL GULF OF MEXICO TO NEAR JAMAICA AND IS
ACCOMPANIED BY DRY UPPER AIR SUPPRESSING CONVECTION OVER MOST OF
THE W CARIBBEAN. THE EXCEPTION IS THAT AN ASSOCIATED...BUT
WEAKENING SURFACE COLD FRONT HAS MOVED OVER CUBA...WITH A
PORTION OF THE FRONT EXTENDING ACROSS THE S-CENTRAL CUBAN
COASTAL WATERS AND CURRENTLY ACCOMPANIED BY TOWERING CUMULUS IN
THE VICINITY OF 21N81W.

AN UPPER ANTICYCLONE CENTERED WELL TO THE SE OF THE CARIBBEAN
NEAR 03N43W RIDGES NW ACROSS VENEZUELA AND N COLOMBIA AND OVER
THE CENTRAL CARIBBEAN...CRESTING ALONG POINTS FROM 10N80W TO
BEYOND 18N64W. ALTHOUGH UPPER LEVEL THIN CIRRIFORM CLOUDS ARE
OBSERVED STREAMING NE ACROSS THE UPPER RIDGE E OF 70W...THE
UPPER LEVELS ARE FOR THE MOST PART QUITE DRY OVER THE E
CARIBBEAN. AT THE LOW LEVELS...LOCALLY BROKEN TRADE WIND
CUMULUS IS RACING W ACROSS THE CARIBBEAN. CLUSTERS OF SHOWERS
ARE NOTED ALONG 17N BETWEEN 66W AND 74W AND ALSO JUST S OF
JAMAICA.


THE ATLANTIC OCEAN...
AN UPPER LEVEL TROUGH IS SWINGING E THROUGH THE SUBTROPICAL ATLC
WITH MEAN ITS AXIS ALONG 70W AT THE MOMENT. A SERIES OF SURFACE
LOW PRES CENTERS ARE NOTED OVER THE CENTRAL N ATLC TO THE E OF
THIS UPPER TROUGH...WITH THE SOUTHERNMOST LOW PRES NEAR 32N64W.
AN ASSOCIATED SURFACE FRONT EXTENDS IN THE AREA ALONG 32N56W TO
THE SE BAHAMAS WHERE THE FRONT BECOMES DIFFUSE...BUT IS STILL
ENHANCING A WELL DEFINED LINE OF SHOWERS AS THE FRONT DIPS
ACROSS CUBA. UPPER DIFFLUENCE IS ENHANCING CONVECTION ALONG THE
COLD FRONT TO THE N OF 27N...BUT LIGHTNING DATA INDICATES THE
CONVECTION IS COMPOSED OF MOSTLY HEAVY SHOWERS THIS MORNING. A
COUPLE MORE SURFACE BOUNDARIES ARE SWINGING CYCLONICALLY AROUND
THE AFOREMENTIONED SURFACE LOW...AND DEFINED BY LOCALLY BROKEN
STRATOCUMULUS CLOUDS SPREADING S OVER THE SUBTROPICS TO THE W OF
65W.

AN UPPER ANTICYCLONE CENTERED NEAR 03N43W RIDGES NE ACROSS THE
CENTRAL ATLC TO BEYOND 32N45W CRESTING NEAR 50N35W. DEBRIS
MOISTURE FROM THE FRONTAL CONVECTION IS ADVECTED ACROSS THIS
UPPER RIDGE COVERING THE UPPER LEVELS OF THE ATLC TO THE N OF
30N E OF 50W...WITH SOME MOISTURE DIVING BACK SE ACROSS THE
RIDGE OVER N AFRICA. AN UPPER TROUGH EXTENDS SW FROM SPAIN
ALONG THE EXTREME NW COAST OF AFRICA TO NEAR 18N37W...AND IS
ACCOMPANIED BY A UPPER DRY AIR WITHIN 180 NM OF ITS AXIS. A
LARGE UPPER ANTICYCLONE OVER AFRICA NEAR 12N13E RIDGES W ALONG
10N INTO THE AREA NEAR 07N30W TAPPING DEBRIS MOISTURE FROM THE
ITCZ CONVECTION...DESCRIBED ABOVE...AND ADVECTING THE MOISTURE
ACROSS N AFRICA TO THE S OF THE UPPER TROUGH. AT THE LOW LEVELS
A SURFACE FRONT IS LOSING IDENTITY ALONG 32N17W TO 27N33W. HIGH
PRES NO THE FRONT NEAR 32N28W RIDGES SW TO 22N55W. LOCALLY OVER
STRATOCUMULUS CLOUDS ARE OBSERVED FROM 05S TO 23N BETWEEN 25W
AND 58W MOVING WSW IN THE ASSOCIATED LOW LEVEL ANTICYCLONIC
FLOW.

$$
NELSON






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