[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 020001
TWDAT

TROPICAL WEATHER DISCUSSION...AMD
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN OCT 01 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 HURRICANE ISAAC AT 02/0000 UTC IS NEAR 37.3N 59.6W
MOVING NORTH-NORTHEAST NEAR 20 KT. THIS POSITION IS ABOUT 715
MILES/1250 KM SOUTH-SOUTHWEST OF CAPE RACE NEWFOUNDLAND.  A TURN
TOWARD THE NORTH-NORTHEAST WITH AN INCREASE IN FORWARD SPEED IS
EXPECTED DURING THE NEXT 24 HOURS. THE ESTIMATED MINIMUM CENTRAL
PRESSURE IS 985 MB. THE MAXIMUM SUSTAINED WIND SPEED IS 70 KT
WITH GUSTS TO 85 KT. ISAAC IS A CATEGORY ONE HURRICANE ON THE
SAFFIR-SIMPSON SCALE.  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 HAS BEGUN RACING NORTHWARD AHEAD OF THE LARGE WRN
ATLC TROUGH WHICH HAS LIKELY MADE THE STORM MORE ASYMMETRIC WITH
MUCH OF ITS CONVECTION TO THE N OF THE CENTER. CONVECTION HAS
INCREASED OVER THE LAST FEW HOURS AND SCATTERED MODERATE COVERS
THE AREA WITHIN 240 NM IN THE NRN SEMICIRCLE AND 90 NM IN THE
SRN SEMICIRCLE. ISAAC WILL BEGIN TO LOSE TROPICAL
CHARACTERISTICS AND IS FORECAST TO BECOME EXTRATROPICAL IN ABOUT
24 HOURS. REGARDLESS OF WHETHER ISAAC IS A TROPICAL OR
EXTRATROPICAL CYCLONE WHEN PASSING NEAR OR OVER
NEWFOUNDLAND...IT WILL LIKELY PRODUCE SUSTAINED WINDS OF
TROPICAL STORM FORCE OVER THAT AREA.

...TROPICAL WAVES/LOWS...
A 1010 MB LOW IS ABOUT 500 NM TO THE SOUTHWEST OF THE CAPE VERDE
ISLANDS NEAR 9N29W. LOW-MID LEVEL ROTATION IS NOTED ON THE LAST
FEW VIS IMAGES AND NIGHT CHANNEL IR. ASSOCIATED SHOWERS AND
TSTMS ARE NOT VERY WELL ORGANIZED AND HAVE BEEN DECREASING IN
INTENSITY OVER THE PAST FEW HOURS. THE ATMOSPHERIC ENVIRONMENT
WILL BECOME VERY HOSTILE NEAR THE SYSTEM AS STRONG SWLY UPPER
LEVEL WINDS WILL INCREASE AHEAD OF A DIGGING SHARP MID-UPPER
LEVEL TROUGH TO THE NW OF THE SYSTEM.

A TROPICAL WAVE IS ALONG 43W S OF 20N MOVING W 15 KT OVER THE
PAST 24 HOURS. THIS WAVE IS NOT VERY ACTIVE ONLY PRODUCING A
SMALL AREA OF SCATTERED SHOWERS AND ISOLATED TSTMS WITHIN 180 NM
EITHER SIDE OF THE WAVE AXIS BETWEEN 12N-14N. DESPITE THE
LIMITED SHOWER ACTIVITY...THE WAVE IS NOT VERY DIFFICULT TO
TRACK WITH LOW-MID LEVEL CYCLONIC TURNING SEEN ON SATELLITE
IMAGERY ABOUT THE AXIS.

A TROPICAL WAVE IS IN THE ERN CARIBBEAN ALONG 67W MOVING W 10 TO
15 KT. THIS WAVE REMAINS FAIRLY WEAK WITH SLIGHT CYCLONIC
VEERING IN THE WINDS FROM ESE E OF THE AXIS TO E OR ENE W OF THE
AXIS. THE INTERACTION BETWEEN THE WAVE AND AN UPPER LOW 150 NM
TO ITS WEST IS PRODUCING SCATTERED SHOWERS AND TSTMS WITHIN 90
NM OF THE AXIS. HOWEVER...MOST OF THIS ACTIVITY HAS DISSIPATED
OVER LAST HOUR OR TWO. MUCH MORE IMPRESSIVE CONVECTIVE ACTIVITY
IS NEAR THE BASE OF THE AXIS OVER S AMERICA HIGHLY CONTRIBUTED
TO THE ITCZ.

A TROPICAL WAVE IS IN THE CENTRAL CARIBBEAN ALONG 77W/78W S OF
21N MOVING W 10 TO 15 KT. CURRENTLY THIS WAVE HAS LITTLE
SIGNATURE IN SFC OBSERVATIONS OR IN SATELLITE IMAGERY. THIS
FEATURE IS LOCATED IN AN AREA OF UPPER DIFFLUENCE BETWEEN A
LARGE UPPER TROUGH TO ITS NW AND A SMALL UPPER LOW TO ITS
EAST...GENERATING SCATTERED SHOWERS AND TSTMS ACROSS
JAMAICA...CUBA AND PARTS OF THE NW CARIBBEAN SEA.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 11N15W 8N32W 12N42W 10N63W. BESIDES
FOR THE AREA OF LOW PRES SW OF THE CAPE VERDE ISLANDS AND THE
TROPICAL WAVE...A SMALL CLUSTER OF MODERATE CONVECTION IS
NEARING THE COAST OF W AFRICA E OF 15W FROM 10N-12N. SCATTERED
MODERATE EXISTS ACROSS A GOOD PORTION OF S AMERICA AND IN THE
SW CARIBBEAN S OF 12N W OF 81W.

...DISCUSSION...
THE GULF OF MEXICO...
THE LARGE DEEP LAYER TROUGH THAT HAS COVERED THE GULF OVER THE
PAST COUPLE OF DAYS HAS PULLED EASTWARD INTO THE WRN ATLC
ALLOWING DEEP RIDGING TO BECOME ESTABLISHED. DIFFLUENT AIR
BETWEEN THIS RIDGE AND A TROUGH OVER MEXICO IS PRODUCING A
CONSIDERABLE AMOUNT OF CLOUDINESS OVER ERN MEXICO SPREADING INTO
THE WRN GULF W OF 91W. ONLY ISOLATED SHOWERS ARE EMBEDDED IN
THIS MOISTURE PLUME. E OF 91W...VERY DRY STABLE AIR IS IN PLACE
KEEPING SKIES FAIR TO MOSTLY CLEAR. THE DRIEST AIR IS IN THE SE
GULF E OF 88W S OF 27N. AT THE SFC...A 1020 MB HIGH IS CENTERED
60 NM S OF THE LOUISIANA COASTLINE NEAR 29N92W. SFC WINDS FLOW
ANTICYCLONIC AROUND THIS HIGH MOSTLY IN THE 10 TO 15 KT RANGE.
THE SFC HIGH IS FORECAST TO MOVE NORTHEAST AND STRENGTHEN
CREATING SLIGHTLY STIFFER EASTERLY WINDS WHICH WILL MOISTEN THE
ATMOSPHERE EARLY THIS WEEK.

THE CARIBBEAN SEA...
THE TAIL END OF THE DEEP WRN ATLC TROUGH EXTENDS INTO THE NW
CARIBBEAN. DIFFLUENCE BETWEEN THIS TROUGH AND AN UPPER LOW 90 NM
S OF HISPANIOLA AND SOME LOW LEVEL CONVERGENCE FROM A NEARBY
TROPICAL WAVE IS GENERATING SCATTERED SHOWERS AND TSTMS ACROSS
THE NW CARIBBEAN INCLUDING JAMAICA...THE CAYMAN ISLANDS AND
CUBA. ISOLATED SHOWERS EXIST ACROSS PUERTO RICO AND THE LESSER
ANTILLES INFLUENCED BY THE UPPER LOW MENTIONED AND AN E
CARIBBEAN TROPICAL WAVE. THE MOST IMPRESSIVE ACTIVITY IS OVER
NRN PORTIONS OF S AMERICA AND THE SW CARIBBEAN HIGHLY
CONTRIBUTED TO THE ITCZ...FOR MORE DETAILS REFER TO THAT
SECTION. TRADE WINDS ARE NEAR 20 KT ACROSS MOST OF THE CARIBBEAN
E OF 78W...WITH SLIGHTER HIGHER WINDS NEAR 25 KT OFF THE N COAST
OF COLOMBIA AND WRN VENEZUELA. A LARGE AREA OF DRY AIR IS IN THE
CENTRAL ATLC ADVECTING INTO THE CARIBBEAN...GFS SUGGESTS THAT
THIS WILL CONTINUE HELPING TO DRY OUT THE CENTRAL AND WRN
CARIBBEAN A LITTLE MON AND TUE.

THE ATLANTIC OCEAN...
AN AMPLIFIED PATTERN EXISTS ACROSS THE ATLANTIC BASIN. A LARGE
DEEP LAYER TROUGH EXTENDS FROM ERN CANADA SOUTHWARD TO THE NW
CARIBBEAN. DRY AIR LIES TO THE W OF THE TROUGH AXIS WITH THE
STRONGEST UPPER CONFLUENCE NEAR THE BASE ACROSS THE WRN BAHAMAS
AND THE SE GULF. A SWATH OF MOISTURE ADVECTED BY A SWLY JET
EXISTS BETWEEN 65W AND 74W. THE SFC FRONTAL BOUNDARY HAS BECOME
LESS DEFINED AND IS NOW ANALYZED A TROF FROM 31N71W TO 24N78W. A
MID-LEVEL SUBTROPICAL RIDGE LIES TO THE E OF THE LARGE TROUGH
AND COVERS THE REGION FROM 42W TO 65W N OF 20N. HURCN ISAAC HAS
REACHED THE WRN EDGE OF THE RIDGE AND IS ACCELERATING NNE AHEAD
OF THE TROUGH. THE SRN PART OF THE SUBTROPICAL RIDGE IS ERODING
DUE TO A FAIRLY LARGE WESTWARD MOVING UPPER LOW CENTERED NEAR
18N50W. THIS UPPER LOW IS THE SRN EXTENSION OF A LARGE TROUGH IN
THE CENTRAL/ERN ATLC WHICH IS ANCHORED BY A LARGE UPPER CYCLONE
NEAR 30N33W AND EXTENDS SW TO THE UPPER LOW NEAR 18N50W. AN
ASSOCIATED SFC FRONT STRETCHES FROM A 1008 MB SFC LOW NEAR THE
AZORES ALONG 31N27W 26N38W. SCATTERED SHOWERS ARE FROM 27N TO
33N BETWEEN 26W AND 35W. IN THE FAR ERN ATLC...A MID-UPPER
ANTICYCLONE IS CENTERED OVER WRN AFRICA NEAR 16N16W WITH RIDGING
EXTENDING TO THE ERN CAPE VERDE ISLANDS.

$$
CANGIALOSI




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