[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 300007
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI SEP 29 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2315 UTC.

...SPECIAL FEATURE...
THE CENTER OF TROPICAL STORM ISAAC AT 29/2100 UTC WAS NEAR 29.7N
56.8W MOVING WEST-NORTHWEST AT 6 KT. THIS GENERAL MOTION IS
EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS WITH A GRADUAL
INCREASE IN FORWARD SPEED. THE ESTIMATED MINIMUM CENTRAL
PRESSURE IS 1000 MB. THE MAXIMUM SUSTAINED WIND SPEEDS HAVE
INCREASED TO 50 KT WITH GUSTS TO 60 KT. SOME ADDITIONAL
STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS... AND ISAAC
COULD BECOME A HURRICANE OVER THE WEEKEND. 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. SCATTERED MODERATE
CONVECTION IN THE FORM OF A BAND ATTEMPTING TO WRAP AROUND THE
CENTER OF ISAAC IS FROM 28N-31N BETWEEN 55W-59W...WITH THE
DEEPEST CONVECTION CURRENTLY IN THE EASTERN SEMICIRCLE NEAR
-63C.

...TROPICAL WAVES...
AN EASTERN ATLANTIC OCEAN TROPICAL WAVE IS ALONG 30W SOUTH OF
20N MOVING WEST NEAR 10 KT. SHORTWAVE IR IMAGERY SHOWS CYCLONIC
TURNING OF THE LOW TO MID CLOUD FIELD ESP. N OF 15N WITHIN 200NM
OF EITHER SIDE OF THE WAVE AXIS. THE DEEPEST CONVECTION
ASSOCIATED WITH THE WAVE IS ALSO ALONG THE NORTHERN
PORTION...WITH A CLUSTER OF SCATTERED MODERATE/ISOLATED STRONG
CONVECTION SEEN FROM 19N-22N BETWEEN 29W-32W. THIS CONVECTION IS
ALSO BEING SUPPORTED BY UPPER DIFFLUENCE BETWEEN THE UPPER LOW
NEAR 26N34W AND THE UPPER HIGH OVER W AFRICA.

A LOW AMPLITUDE ATLANTIC OCEAN TROPICAL WAVE IS ALONG 53W/54W
SOUTH OF 14N MOVING WEST 10 TO 15 KT. THERE IS SOME SUBTLE
CYCLONIC TURNING NOTED IN THIS REGION THOUGH MOST OF THE
CONVECTION IS OFF TO THE W WITH SCATTERED SHOWERS/TSTMS FROM
9N-14N BETWEEN 56W-61W...ALSO A REGION OF UPPER DIFFLUENCE.

AN EASTERN CARIBBEAN SEA/TROPICAL NORTH ATLANTIC TROPICAL WAVE
IS ALONG 64W/65W S OF 24N MOVING W 10 TO 15 KT. A 1013 MB LOW IS
ALONG THE WAVE AXIS NEAR 20N. SHOWERS ACTIVITY ASSOCIATED WITH
THIS WEAK LOW JUST NORTH OF THE VIRGIN ISLANDS HAS DIMINISHED.

A TROPICAL WAVE IS MOVING THROUGH CENTRAL AMERICA AND THE
EASTERN PACIFIC ALONG 89W SOUTH OF 18N MOVING WEST 10-15 KT.
PATCHES OF SCATTERED MODERATE CONVECTION ARE AFFECTING CENTRAL
AMERICA AND THE EPAC WITH MINIMAL SHOWERS/TSTM ACTIVITY NOTED
OVER THE WRN CARIBBEAN.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N16W 13N29W 10N40W 9N60W.  OUTSIDE
THE CONVECTION MENTIONED IN THE TROPICAL WAVE SECTION...
SCATTERED MODERATE CONVECTION IS ALONG THE W COAST OF AFRICA AND
ADJACENT ATLC WATERS FROM 6N-13N BETWEEN 11W-17W. ISOLATED
SHOWERS/TSTMS ARE NOTED ELSEWHERE WITHIN 150NM OF THE AXIS.

...DISCUSSION...
THE GULF OF MEXICO...
A COLD FRONT EXTENDS THROUGH CENTRAL FLORIDA AND THE CENTRAL
GULF ALONG 27N82W 27N80W...AND THEN BECOMES STATIONARY TO THE
MIDDLE COAST OF TEXAS. PLACEMENT OF THE FRONT WAS PRIMARILY
BASED ON THE ASSOCIATED THIN ROPE CLOUD IN THE VICINITY. DEEP
CONVECTION IS MINIMAL ASIDE FROM A CLUSTER OF SCATTERED MODERATE
CONVECTION OVER COASTAL TEXAS AND NW GULF FROM 27N-30N BETWEEN
94W-97W. MID TO UPPER LEVEL WESTERLY FLOW DOMINATES THE MAJORITY
OF THE GULF TONIGHT ON THE SOUTHERN PERIPHERY OF THE LARGE
LONGWAVE TROUGH OVER THE EASTERN THIRD OF THE COUNTRY. MID TO
UPPER LEVEL ANTICYCLONIC MOTIONS ARE SEEN IN WV IMAGERY OVER THE
WRN BAY OF CAMPECHE ASSOCIATED WITH A MID TO UPPER HIGH OVER
CENTRAL MEXICO. THERE ARE A FEW ISOLATED SHOWERS/TSTMS IN THE
BAY OF CAMPECHE FROM UPPER DIFFLUENCE BETWEEN THE HIGH OVER
MEXICO AND THE TROUGHING OVER THE EASTERN USA. MUCH OF THE
REMAINDER OF THE GULF IS UNDER THE INFLUENCE OF DRY MID TO UPPER
LEVEL AIR AND FAIR WEATHER...ALONG WITH A 1019MB SURFACE HIGH
BUILDING INTO THE NORTHERN GULF FROM ITS CENTER OVER NE
LOUISIANA.

THE CARIBBEAN SEA...
FLOW AROUND A MID TO UPPER HIGH SPINNING OVER CENTRAL AMERICA IS
AFFECTING THE WRN CARIBBEAN THIS EVENING. AN UPPER RIDGE EXTENDS
NE THROUGH THE NW CARIBBEAN...CUBA AND THE BAHAMAS. UPPER
DIFFLUENCE BETWEEN THIS FEATURE AND THE LARGE TROUGH OVER THE
EASTERN UNITED STATES IS HELPING TO SUPPORT THE ISOLATED
SHOWERS/TSTMS OVER THE NW CARIBBEAN FROM 14N-23N BETWEEN
77W-88W. MUCH OF THE REMAINDER OF THE CARIBBEAN IS FAIRLY QUIET
THIS EVENING. THERE IS AN UPPER LOW NEAR ERN DOMINICAN REPUBLIC
WHICH MAY BE HELPING THE SHOWERS/TSTMS N/NW OF RINCON PUERTO
RICO SEEN ON THE SAN JUAN DOPPLER RADAR...ALONG WITH ITS
INTERACTION WITH THE WAVE/LOW AFFECTING THE VIRGIN ISLANDS. 15
TO 20 KT TRADES PERSIST THIS EVENING WITH SW PORTION OF THE ATLC
HIGH INTERACTING WITH LOWER PRESSURE NEAR THE COLOMBIAN COAST.

THE ATLANTIC OCEAN...
A COLD FRONT EXTENDS THROUGH CENTRAL FLORIDA AND THE SW NORTH
ATLC ALONG 27N80W 32N75W. PLACEMENT OF THIS FRONT IS BASED ON
THE SUBTLE ROPE CLOUD SEEN ON THE LAST FEW PICTURES OF VISIBLE
IMAGERY THIS EVENING. THE CLOUDINESS AND SHOWERS AHEAD OF THIS
FRONT FROM 22N-32N BETWEEN 70W-80W SEEM MORE ASSOCIATED WITH THE
OLD FRONTAL BOUNDARY WE HAVE BEEN TRACKING THE LAST SEVERAL
DAYS. A TROUGH IS ANALYZED AHEAD OF THE FRONT THAT IS NOW BEING
DUBBED A PREFRONTAL TROUGH...ALONG 23N79W 31N71W AND WAS
CAPTURED FAIRLY WELL BY THIS MORNINGS QUIKSCAT PASS. REGARDLESS
OF ITS TITLE IT APPEARS THESE TWO FEATURES MAY BE BECOMING A
SINGLE ENTITY. THE ASSOCIATED CLOUDINESS/SHOWERS ARE ALSO BEING
SUPPORTED BY UPPER DIFFLUENCE BETWEEN AN UPPER RIDGE EXTENDING
NE THROUGH THE SE BAHAMAS AND THE DEEP TROUGHING OVER THE
EASTERN THIRD OF THE COUNTRY. GOES UPPER LEVEL WINDS SHOW BETTER
OUTFLOW OVER ISAAC THAN LAST EVENING. THERE IS A MID TO UPPER
LEVEL ANTICYCLONE NE OF THE LEEWARD ISLANDS NEAR 23N54W. A PAIR
OF UPPER LOWS ARE SEEN IN THE ERN ATLC NEAR 20N43W AND 26N34W.
THERE IS A REFLECTION OF THE WRN MOST OF THESE UPPER LOWS AT THE
SURFACE AS A TROUGH ALONG 20N42W 28N42W WITH A WEAK 1014 SURFACE
LOW ALONG THE TROUGH NEAR 24N. AN UPPER HIGH OVER WRN AFRICA IS
DOMINATING THE MID TO UPPER LEVELS OVER THE FAR ERN ATLC.


$$
WILLIS




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