[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 301049
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SAT SEP 30 2006

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHEASTERN
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...WEATHER OBSERVATIONS...RADAR...
AND METEOROLOGICAL ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 1115 UTC.

...SPECIAL FEATURES...
THE CENTER OF TROPICAL STORM ISAAC AT 30/0900 UTC IS NEAR 30.3N
58.0W MOVING WEST-NORTHWEST AT 6 KT. THE ESTIMATED MINIMUM
CENTRAL PRESSURE IS 995 MB. THE MAXIMUM SUSTAINED WIND SPEEDS
ARE 60 KT WITH GUSTS TO 75 KT. PLEASE READ THE LATEST NHC
FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC
AND THE PUBLIC ADVISORY UNDER MIATCPAT4/WTNT34 KNHC FOR MORE
DETAILS. ISAAC LOOKS MUCH MORE TROPICAL THAN IT DID 24 HR
AGO...WITH CONVECTIVE TOPS COLDER THAN -60C NOT FAR NORTHWEST OF
THE CENTER AND THE FIRST SIGNS OF A 30-35 NM WIDE EYE. A BAND OF
MODERATE TO STRONG CONVECTION IS WRAPPING AROUND THE CENTER.
SOME STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS...AND
ISAAC COULD BECOME THE FIFTH HURRICANE OF THE SEASON LATER
TODAY. INTERESTS IN BERMUDA...THE CANADIAN MARITIME
PROVINCES...AND NEWFOUNDLAND SHOULD MONITOR THE PROGRESS OF
ISAAC.

...TROPICAL WAVES...
TROPICAL WAVE IS ALONG 31/32W SOUTH OF 20N MOVING WEST 10 KT. A
CYCLONIC TURNING IS SEEN AT LOW LEVELS. SCATTERED SHOWERS ARE ON
THE NORTHERN END OF THE WAVE AXIS AND WITHIN THE ITCZ.

TROPICAL WAVE IS ALONG 59W SOUTH OF 16N MOVING WEST 10 KT.
SCATTERED SHOWERS AND ISOLATED TSTMS ARE MAINLY AHEAD OF THE
WAVE A AXIS FROM 10N-14N BETWEEN 58W-63W. THIS WAVE IS ALREADY
PRODUCING LIGHT SHOWERS OVER THE WINDWARD ISLANDS.

A TROPICAL WAVE IS OVER PUERTO RICO ALONG 67W MOVING WEST AT 10
TO 15 KT. THIS WAVE WILL REACH DOMINICAN REPUBLIC THIS MORNING.
ST.CROIX REPORTED HEAVY RAIN WITH THE PASSAGE OF THE WAVE. THE
SAN JUAN DOPPLER RADAR IS SHOWING SCATTERED TO NUMEROUS SHOWERS
WITH EMBEDDED TSTMS ACROSS THE U.S VIRGIN ISLANDS MOVING INTO
THE EASTERN PORTION OF PUERTO RICO AS WELL AS ACROSS THE COASTAL
WATERS. THE NORTHERN END OF THE WAVE IS INTERACTING WITH AN
UPPER LOW LOCATED NEAR 20N64W. A CLUSTER OF MODERATE TO ISOLATED
STRONG CONVECTION IS FROM 23N-26W BETWEEN 63W-65W.

A TROPICAL WAVE IS INLAND OVER THE YUCATAN PENINSULA AND
GUATEMALA INTO THE EPAC. IT AXIS LIES ALONG 91W SOUTH OF 20N
MOVING WEST 10-15 KT. CLUSTERS OF MODERATE/ISOLATED STRONG
CONVECTION HAS DEVELOPED ALONG THE PACIFIC COAST FROM NICARAGUA
TO GUATEMALA AND OVER THE GULF OF TEHUANTEPEC.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N16W 12N29W 11N35W 10N45W 11N58W.
OUTSIDE THE CONVECTION MENTIONED IN THE TROPICAL WAVE SECTION...
SCATTERED MODERATE CONVECTION IS FROM 4N-11N EAST OF 30W.
ISOLATED SHOWERS ARE SEEN ELSEWHERE.

...DISCUSSION...
THE GULF OF MEXICO...
AS OF 0900 UTC...A COLD FRONT ENTERS THE AREA NEAR 31N70W THEN
CONTINUES SOUTHWESTWARD ACROSS SOUTH FLORIDA. DOPPLER RADAR
SHOWS A LINE OF SHOWERS WITH EMBEDDED TSTMS ALONG THE FLORIDA
KEYS AND JUST EAST OF THE CITY OF MIAMI OVER THE OCEAN. A
PREFRONTAL TROUGH EXTENDS FROM 29N72W TO CENTRAL CUBA NEAR
22N80W. SCATTERED MODERATE CONVECTION IS BETWEEN THE COLD FRONT
AND THE PREFRONTAL TROUGH. SIMILAR CONVECTION IS  ALSO BETWEEN
CUBA AND THE BAHAMAS. IN THE UPPER LEVELS...THE BASE OF A
LONGWAVE TROUGH OVER THE EASTERN U.S. IS OVER THE GULF OF MEXICO
MOVING E. ABUNDANT UPPER LEVEL MOISTURE COVERS THE MAJORITY OF
MEXICO. DRY AIR IS OVER THE NORTHERN GULF WATERS. A STRONG HIGH
PRESSURE WILL BUILD OVER THE AREA DURING THE NEXT FEW DAYS WITH
INCREASING EASTERLY WINDS.

THE CARIBBEAN SEA...
MODERATE TRADEWINDS ARE BLOWING ACROSS THE CARIBBEAN SEA.
WIDELY SCATTERED MODERATE CONVECTION IS OVER THE NW CARIBBEAN
WEST OF 80W AND NORTH OF JAMAICA. AN UPPER HIGH SITUATED NEAR
10N86W. A RIDGE EXTENDS NE FROM THIS ANTICYCLONE ACROSS THE NW
CARIBBEAN...CUBA AND THE BAHAMAS TO 27N68W. THIS FEATURE ALSO
COVERS CENTRAL AMERICA...SUPPORTING THE DEVELOPMENT OF MODERATE
TO STRONG CONVECTION OVER THE SW CARIBBEAN...PANAMA...NORTHERN
COLOMBIA AND THE GULF OF FONSECA. AN UPPER LOW IS CENTERED
OVER HISPANIOLA NEAR 18N68W. A TROUGH RUNS FROM THE LOW TO
WESTERN VENEZUELA. THE TRADE WINDS WILL SLIGHTLY INCREASE ON
SUNDAY ACROSS THE CENTRAL CARIBBEAN SOUTH OF 15N.

THE ATLANTIC OCEAN...
A COLD FRONT IS OVER THE W ATLANTIC ALONG 31N70W 27N76W THEN
CONTINUES ACROSS THE NORTHERN BAHAMAS AND SOUTH FLORIDA. A
PREFRONTAL TROUGH EXTENDS FROM 29N72W TO CENTRAL CUBA NEAR
22N80W. A RIDGE COVERS THE SE U.S. AND NORTHERN FLORIDA. AN
UPPER TROUGH IS ENTERING THE NW CORNER OF THE AREA SUPPORTING
THE COLD FRONT MENTIONED ABOVE. A RIDGE IS JUST SE OF THIS
TROUGH AND EXTENDS FROM A HIGH LOCATED NEAR 10N86W ACROSS CUBA
AND THE BAHAMAS. A PAIR OF UPPER LOWS ARE SEEN IN THE
EAST-CENTRAL ATLC NEAR 20N44W AND 27N32W. A SURFACE TROUGH...
REFLECTION OF THE WRN MOST OF THESE UPPER LOWS GOES FROM 25N44W
TO 16N47W. SOME CYCLONIC TURNING IS ALSO SEEN IN THE LOW LEVELS.
OVER THIS AREA. AN UPPER RIDGE DOMINATES THE E ATLC AND WEST
AFRICA. CLOUDINESS AND ISOLATED SHOWERS COVER AN AREA FROM
20N-30N EAST OF 35W TO THE CANARY ISLANDS.

$$
GR


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