[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 301757
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN SEP 30 2007

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
SECTIONS OF SOUTH AMERICA...AND THE 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.

...SPECIAL FEATURE...

MELISSA IS DOWNGRADED TO A TROPICAL DEPRESSION AT 30/1500 UTC.
AT THIS TIME...IT WAS CENTERED NEAR 16.1N 32.6W OR ABOUT 495 NM
WEST OF THE CAPE VERDE ISLANDS...MOVING WNW AT 11 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 1007 MB.  MAXIMUM SUSTAINED WIND
SPEED IS 25 KT WITH GUSTS TO 35 KT. SEE LATEST NHC FORECAST
ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC AND THE
PUBLIC ADVISORY UNDER MIATCPAT4/WTNT34 KNHC FOR MORE DETAILS.
AFTER MOST OF THE CONVECTION DISSIPATED ABOUT 12 HOURS AGO...THE
CYCLONE HAS ONLY BEEN ABLE TO GENERATE SMALL PULSATING BURSTS OF
CONVECTION. STRONG WESTERLY SHEAR PERSISTS OVER THE STORM.
THE ENVIRONMENT AHEAD OF MELISSA IS EXPECTED TO REMAIN HOSTILE AS
WESTERLY SHEAR IS FORECAST TO PERSIST. THE NHC INTENSITY
FORECAST MAINTAINS MELISSA AS A TROPICAL DEPRESSION DURING THE
NEXT DAY OR SO. PRESENTLY A SMALL CLUSTER OF MODERATE CONVECTION
IS NEAR 16N32W.

...TROPICAL WAVES...

TROPICAL WAVE IS OFF THE COAST OF W AFRICA ALONG 22W S OF 15N
MOVING W 10-15 KT. THE MIMIC TPW ANIMATION SHOWS A MODEST SURGE
OF MOISTENED AIR JUST SOUTH OF THE CAPE VERDE ISLANDS. SATELLITE
DERIVED WINDS SHOW VERY WELL THE WIND SHIFT ASSOCIATED WITH THE
WAVE. SCATTERED MODERATE CONVECTION IS MAINLY NEAR THE
INTERSECTION OF THE WAVE AND THE ITCZ FROM 4N-7N BETWEEN
20W-24W...WITH ISOLATED SHOWERS WITHIN 100 NM AHEAD OF THE WAVE
AXIS FROM 8N-11N.

TROPICAL WAVE IS ALONG 40W S OF 16N MOVING W 15 KT. INVERTED-V
LOW LEVEL SIGNATURE IS OBSERVED ON VIS IMAGERY. THERE IS ALSO A
WEAK NWD PERTURBATION IN THE ITCZ THAT IS NOTED ON THE MIMIC TPW
ANIMATION. CONVECTION IS MAINLY CONFINED TO THE ITCZ. SCATTERED
SHOWERS ARE FROM 4N-7N BETWEEN 38W-42W.

A WEAK TROPICAL WAVE IS OVER CENTRAL AMERICA ALONG 89W S OF 20N
MOVING W 10-15 KT. THE WAVE...COUPLED WITH A DIFFLUENT PATTERN
ALOFT IS GENERATING SCATTERED SHOWERS AND TSTMS OVER THE GULF OF
HONDURAS. THE WAVE ALSO EXTENDS INTO THE EPAC WHERE IS PRODUCING
SIMILAR SHOWER ACTIVITY.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 7N15W 4N27W 7N37W 7N45W 8N60W.
OUTSIDE OF THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES...
WIDELY SCATTERED MODERATE CONVECTION IS FROM 2N-5N BETWEEN
14W-21W. SCATTERED MODERATE CONVECTION IS FROM 2N-6N BETWEEN
30W-38W.

DISCUSSION...

GULF OF MEXICO...
A WEAKENING FRONTAL BOUNDARY MOVED ACROSS SOUTH FLORIDA AND THE
SE GULF EARLY THIS MORNING A NOW IS REACHING THE CITY OF HAVANA
CUBA. NUMEROUS SHOWERS AND TSTMS WERE REPORTED IN SOUTH FLORIDA
WITH THE PASSAGE OF THE FRONTAL BOUNDARY. CURRENTLY...A NARROW
BAND OF SHOWERS AND TSTMS IS AFFECTING WESTERN CUBA. WINDS ARE
ON THE INCREASE BEHIND THE FRONTAL SYSTEM WITH THE FLORIDA KEYS
ALREADY REPORTING GUSTY WINDS OF 25 KT. COMPUTER MODELS HAVE A
WEAK LOW DEVELOPING ALONG THE FRONTAL BOUNDARY OVER THE
BAHAMAS...THEN THE LOW IS FORECAST TO MOVE WWD ACROSS THE
FLORIDA KEYS LATE MONDAY THROUGH TUESDAY. STRONG HIGH PRESSURE
FOLLOWS THE FRONT WITH A 1034 MB HIGH OVER NEW ENGLAND. THIS
HIGH EXTENDS A RIDGE SW COVERING THE EASTERN U.S. AND NORTHERN
GULF WATERS N OF 25 N. AS A RESULT...THE NE QUADRANT OF THE GULF
HAS NELY SURFACE FLOW OF 20 TO 25 KT WITH BUILDING SEAS. UNDER
THE INFLUENCE OF THE SFC RIDGE MOSTLY FAIR WEATHER PREVAILS. A
SFC TROUGH IS ANALYZED OVER THE BAY OF CAMPECHE AND THE SW GULF.
SHOWER ACTIVITY IS MINIMAL ASSOCIATED WITH THIS TROUGH. IN THE
UPPER LEVELS...AN UPPER HIGH LOCATED OVER NORTH-CENTRAL MEXICO
COVERS THE WESTERN GULF...INCLUDING THE BAY OF CAMPECHE AND THE
YUCATAN PENINSULA. AN UPPER TROUGH CROSSES THE STRAITS OF
FLORIDA AND THE FAR SE GULF WITH A DEVELOPING UPPER LOW OVER THE
NW BAHAMAS. MID/UPPER DRY DOMINATES MOST OF THE EASTERN GULF AND
THE FLORIDA PENINSULA...THUS A DECREASING TREND IN SHOWER/TSTM
ACTIVITY IS EXPECTED OVER SOUTH FLORIDA THIS AFTERNOON. THE
MENTIONED UPPER TROUGH IS SUPPORTING THE FRONTAL SYSTEM OVER
WESTERN CUBA. MOIST ONSHORE FLOW IS PRODUCING SOME SHOWER
ACTIVITY OVER THE NW CORNER OF THE GULF AND THE COAST OF TEXAS.

CARIBBEAN SEA...
SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS OVER THE
CARIBBEAN PLAINS OF NICARAGUA AND ADJACENT REGIONAL WATERS. THIS
ACTIVITY IS ASSOCIATED WITH A MOIST LOW LEVEL FLOW AND UPPER
DIFFLUENCE BETWEEN AN UPPER RIDGE THAT EXTENDS SE FROM AN UPPER
HIGH ANCHORED OVER NORTH-CENTRAL MEXICO...AND A SHORT WAVE
TROUGH OVER E CUBA/JAMAICA. SIMILAR CONVECTION IS ALSO SEEN
BETWEEN HAITI AND JAMAICA ASSOCIATED WITH THE SHORT WAVE TROUGH
AND A SURFACE TROUGH THAT EXTENDS FROM THE W ATLC INTO THE
CARIBBEAN THROUGH THE WINDWARD PASSAGE. MORE ABOUT THIS TROUGH
IN THE ATLANTIC SECTION. THE WEATHER PATTERN OVER THE EASTERN
CARIBBEAN HAS NOT CHANGED DURING THE LAST FEW DAYS. NWLY WINDS
ASSOCIATED WITH AN UPPER LOW LOCATED NEAR 20N60W ARE ADVECTING
HIGH CLOUDS/MID TO UPPER-LEVEL MOISTURE OVER PUERTO RICO AND THE
NE CARIBBEAN INTO THE LESSER ANTILLES. THESE WINDS...PAIRED WITH
THE LOCAL EFFECTS ARE HELPING TO INDUCE SCATTERED SHOWERS AND
TSTMS OVER THE AREA...PARTICULARLY DURING THE AFTERNOON AND
EARLY EVENING HOURS. AN UPPER RIDGE EXTENDING NE FROM AN UPPER
HIGH LOCATED NEAR NORTHERN COLOMBIA IS ALSO SUPPORTING SOME
CONVECTIVE ACTIVITY OVER HISPANIOLA. TRADEWINDS REMAIN LIGHT TO
MODERATE ACROSS THE BASIN.

ATLANTIC OCEAN...
THERE ARE THREE AREAS OF INTEREST IN THE ATLANTIC FORECAST AREA.
FIRST...T.D. MELISSA. SEE SPECIAL FEATURE. SECOND...THE REMNANTS
OF KAREN...LOCATED A COUPLE HUNDRED EAST OF LEEWARD ISLANDS...
WHICH ARE INTERACTING WITH AN UPPER-LEVEL TROUGH. THIS IS
PRODUCING A LARGE AREA OF DISORGANIZED SHOWERS AND TSTMS. A SFC
TROUGH IS ANALYZED IN THIS AREA AND RUNS FROM THE WINDWARD
ISLANDS ALL THE WAY NE TO 21N51W. A WEAK 1012 MB LOW IS ALONG
THE TROUGH AXIS NEAR 16N58W. VIS SATELLITE IMAGERY SHOWS A SWIRL
OF LOW CLOUDS RELATED TO THIS LOW. UPPER-LEVEL WINDS ARE
CURRENTLY UNFAVORABLE FOR REGENERATION OF THIS SYSTEM...BUT THEY
COULD BECOME A LITTLE MORE FAVORABLE DURING THE NEXT DAY OR TWO
AS THIS SYSTEM MOVES NORTHWESTWARD AT 10 TO 15 MPH. THIRD...A
LARGE AREA OF DISORGANIZED CLOUDINESS AND THUNDERSTORMS ARE
LOCATED OVER THE WESTERN ATLANTIC...BAHAMA ISLANDS...AND
PORTIONS OF SOUTH FLORIDA. THIS ACTIVITY IS ASSOCIATED WITH A
SURFACE TROUGH AND THE ABOVE MENTIONED FRONTAL BOUNDARY. SOME
SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE DURING THE NEXT
SEVERAL DAYS AS IT MOVES SLOWLY WESTWARD TOWARD THE STRAITS OF
FLORIDA AND THE FLORIDA KEYS. A COLD FRONT ALSO CLIPS THE
FORECAST AREA ALONG 30N BETWEEN 25W AND 35W. A NARROW BAND OF
SHOWERS IS ASSOCIATED WITH THE FRONT. A SFC RIDGE CONTROLS THE
REMAINDER OF THE ATLC. IN THE UPPER LEVELS...A TROUGH IS OVER
THE W ATLANTIC AND THE STRAITS OF FLORIDA. A RIDGE IS JUST E OF
THE TROUGH. THESE UPPER FEATURES ARE ENHANCING CONVECTION OVER
THE W ATLC AND THE BAHAMAS. A LARGE UPPER LEVEL LOW IS CENTERED
NEAR 20N60W PRODUCING THE SW SHEAR OVER THE REMNANTS OF KAREN.
WLY FLOW IS OVER THE E ATLANTIC N OF 20N E OF 40W. A LARGE UPPER
LEVEL HIGH IS OVER THE TROPICS JUST EAST OF THE CAPE VERDE
ISLANDS.

$$
GR






This weather bulletin was brought to you by:
www.nashvilleweather.net