[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 181758
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT TUE OCT 18 2005

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN SECTIONS
OF SOUTH AMERICA...AND 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURE...

HURRICANE WILMA IS CENTERED NEAR 16.7N 81.1W...OR 155 NM S OF
GRAND CAYMAN...AT 18/1800 UTC MOVING WNW 7 KT. MAXIMUM SUSTAINED
WINDS HAVE INCREASED TO 70 KT WITH GUSTS TO 80 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 975 MB. SEE LATEST NHC FORECAST/
ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC AND THE
PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT4/WTNT34 KNHC
FOR MORE DETAILS. WILMA WAS UPGRADED TO HURRICANE STATUS THIS
MORNING AND IS WELL ON ITS WAY TO STRENGTHENING TO A MAJOR
HURRICANE OVER THE NEXT SEVERAL DAYS. DEEP CONVECTION HAS BEEN
MAINTAINED WITHIN 45 NM OF THE CENTER AND THERE HAVE BEEN HINTS
OF A DIMPLE FEATURE WITHIN THE CENTRAL DENSE OVERCAST...
FORESHADOWING THE DEVELOPMENT OF AN EYE. AN UPPER LEVEL TROUGH
LIES OVER THE NW QUADRANT OF THE STORM FROM W/CNTRL CUBA TO THE
GULF OF HONDURAS AND HAS BEEN AFFECTING WILMA WITH DRIER AIR AND
SOME INCREASED SHEAR...BUT THESE EFFECTS APPEAR TO BE LESSENING
AS CONVECTION FILLS IN AROUND THE ENTIRE CIRCULATION. SCATTERED
MODERATE/ STRONG CONVECTION IN SPIRAL BANDS FROM 12N-19N BETWEEN
77W-86W. SCATTERED MODERATE/STRONG ALSO CONTINUES TO DEVELOP NE
OF WILMA FROM 15N-21N BETWEEN 74W-80W INCLUDING OVER JAMAICA...
EXTENDING THE THREAT FOR FLASH FLOODING ON THE ISLAND.

...TROPICAL WAVES...

CENTRAL ATLANTIC TROPICAL WAVE IS ADDED ALONG 42W S OF 15N
MOVING W 15 KT. THE WAVE IS ADDED BASED ON A LONG-TERM LOOP OF
SATELLITE IMAGERY WHICH SHOWS A CONTINUOUS CONVECTIVE CLUSTER...
AND GFS MODEL GUIDANCE WHICH SHOWS A LOW AMPLITUDE WIND SHIFT AT
700 MB. THE WAVE ALSO APPEARS TO BE ALONG THE LEADING EDGE OF AN
EASTERLY SURGE...WITH SAHARAN DUST EXTENDING E OF THE AXIS TO
AFRICA AND MID-LEVEL 700 MB WINDS INCREASING TO 35 KT. WIDELY
SCATTERED MODERATE CONVECTION FROM 8N-13N BETWEEN 36W-46W.

TROPICAL WAVE LOCATED ABOUT 500 NM E OF THE LESSER ANTILLES
ALONG 52W S OF 21N MOVING W 15 KT. THE WAVE HAS A BROAD
CIRCULATION WITH SEVERAL LOW-LEVEL SWIRLS ROTATING ALONG AND TO
THE E OF THE AXIS. ONLY ISOLATED SHOWERS ARE FROM 12N-15N
BETWEEN 49W-53W.

EAST CARIBBEAN TROPICAL WAVE ALONG 66W S OF 15N MOVING W 15 KT.
UPPER AIR DATA FROM BARBADOS AND TRINIDAD BOTH SHOW A LOW TO
MID-LEVEL PERTURBATION PASSING THE ISLANDS A LITTLE MORE THAN A
DAY AGO. THE WAVE HAS LOST ALL THE DEEP CONVECTION IT HAD
YESTERDAY AND ALL THAT IS LEFT IS ISOLATED SHOWERS/TSTMS FROM
13N-15N BETWEEN 64W-68W.

WEST CARIBBEAN TROPICAL WAVE ALONG 77W/78W S OF 13N MOVING W
10-15 KT. THE WAVE IS MOVING W BENEATH HURRICANE WILMA...CAUSING
IT TO LACK MUCH IF ANY SIGNATURE. THE CURRENT POSITION IS BASED
PRIMARILY ON A CLUSTER OF CONVECTION ALONG THE PACIFIC COAST OF
COLOMBIA.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 7N10W 3N23W 5N40W 14N50W...THEN
ALONG 7N53W 8N65W. WIDELY SCATTERED MODERATE CONVECTION FROM
4N-9N BETWEEN 10W-19W. WIDELY SCATTERED MODERATE...PARTLY
ASSOCIATED WITH TROPICAL WAVES...WITHIN 120 NM OF THE AXIS
BETWEEN 33W-49W.

...DISCUSSION...

GULF OF MEXICO...
THERE HAS BEEN LITTLE CHANGE TO THE UPPER AIR PATTERN SINCE THIS
TIME YESTERDAY. A LARGE AND SUBSIDENT UPPER LEVEL HIGH HAS
SHIFTED A LITTLE TO THE W AND IS CENTERED NEAR CABO ROJO MEXICO.
THE SHIFT IN THE HIGH HAS ALLOWED BROAD NWLY FLOW TO SWEEP IN
FROM THE N GULF COAST EWD ACROSS FLORIDA...INTO THE BASE OF A
TROUGH LOCATED OVER THE W ATLC. THE ATMOSPHERE IS DRY (WITH
PRECIPITABLE WATER AS LOW AS 0.75" NEAR THE LOUISIANA/
MISSISSIPPI COAST) AND ONLY PROGRESSIVELY MOISTENS UP SWD TO
ABOUT 2.00" NEAR THE YUCATAN CHANNEL. AS SUCH...SKIES ARE CLEAR
N OF 26N AND ONLY A FEW SHOWERS ARE NOTED OVER THE BAY OF
CAMPECHE MOVING S TO THE ISTHMUS OF TEHUANTEPEC. MOISTURE AND
ASSOCIATED CLOUDS/SHOWERS WILL BEGIN TO INCREASE OVER THE SE
GULF ESPECIALLY LATE WED INTO THU AS HURRICANE WILMA APPROACHES
FROM THE CARIBBEAN.

CARIBBEAN...
WILMA HAS STRENGTHENED TO A HURRICANE OVER THE W/CENTRAL
CARIBBEAN AND HAS A LARGE CONVECTIVE ENVELOPE WHICH EXTENDS FROM
THE HONDURAS AND NICARAGUAN COASTS NEWD THROUGH E CUBA. SEE
SPECIAL FEATURES FOR FURTHER DISCUSSION ON WILMA. AN UPPER RIDGE
EXTENDS NE OF THE HURRICANE ACROSS PUERTO RICO AND THE NRN
LEEWARD ISLANDS AND CIRRUS OUTFLOW HAS SPREAD FROM THE SW ATLC
SWD ACROSS THE E CARIBBEAN. DRIER AIR IS GRADUALLY MOVING IN
FROM THE E AND SKIES ARE ONLY PARTLY CLOUDS E OF 70W WITH AN
OCCASIONAL PASSING SHOWER. SHOWERS/TSTMS ARE EXPECTED TO BEGIN
SPREADING ACROSS THE LESSER ANTILLES THU NIGHT AND FRI ALONG A
TROPICAL WAVE MOVING IN FROM THE ATLC.

WEST ATLANTIC...
A BROAD UPPER TROUGH...ANCHORED BY A POLAR VORTEX OVER
NEWFOUNDLAND...EXTENDS SWD OVER FLORIDA AND THE W ATLC WATERS TO
25N. THE SUBTROPICAL JET LIES ON THE SE SIDE OF THE TROUGH FROM
CNTRL CUBA NEWD ACROSS THE BAHAMAS TO 32N58W. A DEEP TROPICAL
MOISTURE PLUME EXTENDS UP TO 400 NM SE OF THE JET AND IS
INTERACTING WITH A SURFACE TROUGH TO PRODUCE SCATTERED MODERATE
CONVECTION FROM 23N-27N BETWEEN 64W-72W. THE TROUGH LIES ALONG
32N52W 26N70W 25N78W 21N82W AND THE WRN END IS LIFTING NWD
ACROSS THE NRN BAHAMAS AND FLORIDA (ALMOST LIKE A PSEUDO WARM
FRONT). ISOLATED SHOWERS/TSTMS ARE BEING TRIGGERED BY THIS
BOUNDARY FROM THE NRN BAHAMAS WWD INTO THE FLORIDA STRAITS AND
EXTREME S FLORIDA.

EAST/CENTRAL ATLANTIC...
A WEAKENING UPPER LEVEL LOW IS CENTERED JUST NE OF THE NRN
LEEWARD ISLANDS NEAR 19N58W BUT IT NO LONGER HAS ENOUGH DYNAMICS
TO SUPPORT ANY DEEP CONVECTION. A SECOND UPPER LOW IS CENTERED
NEAR 21N46W AND IS MOVING WWD BENEATH THE AXIS OF AN UPPER RIDGE
LYING ALONG 22N55W 32N35W. A WEAK 1018 MB LOW CENTERED NEAR
25N42W CONTINUES TO SLIDE NW 10 KT BUT IS QUICKLY DISSIPATING
WITH MOST OF THE SHOWER ACTIVITY DIMINISHING. FARTHER E...A
VIGOROUS UPPER LOW IS LIFTING NEWD ACROSS MOROCCO INTO NRN
ALGERIA WITH ITS ASSOCIATED TROUGH LAGGING BEHIND TO 24N15W
20N30W. AN UPPER LEVEL RIDGE LIES ACROSS THE TROPICS ALONG 8N
WITH A BELT OF UPPER LEVEL WESTERLIES EXTENDING BETWEEN 45W AND
THE AFRICAN COAST...WITH SPEEDS 50-60 KT AT 200-300 MB.
WIDESPREAD SAHARAN DUST IS EMBEDDED IN THE LOW-LEVEL EASTERLIES
FROM 8N-21N E OF 45W.

$$
BERG


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