[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 192359
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE SEP 19 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 FEATURES...
AT 20/000O UTC GORDON IS NEARING THE CENTRAL AZORES. IT IS
CENTERED NEAR 37.8N 30.0W OR ABOUT 170 MILES WEST-SOUTHWEST OF
THE ISLAND OF TERCEIRA IN THE AZORES RACING EASTWARD AT 29 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 979 MB. MAXIMUM SUSTAINED
WIND SPEED IS 75 KT WITH GUSTS TO 90 KT. SEE THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
OR THE PUBLIC ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE
DETAILS. GORDON WILL MOVE NEAR OR OVER THE CENTRAL AND EASTERN
ISLANDS OF THE AZORES TONIGHT AND EARLY WEDNESDAY AND WILL BE
NEARING PORTUGAL AND NORTHWEST SPAIN LATE WEDNESDAY AS A STRONG
EXTRATROPICAL CYCLONE. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS MAINLY NORTH OF THE CENTER FROM 37N-39N BETWEEN
30W-32W.

HURRICANE HELENE IS CENTERED NEAR 24.6N 54.1W OR ABOUT 840 MILES
SOUTHEAST OF BERMUDA AT 19/2100 UTC MOVING WEST-NORTHWEST AT 8
KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 956 MB. MAXIMUM
SUSTAINED WIND SPEED IS 95 KT WITH GUSTS TO 115 KT. SEE THE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/
WTNT23 KNHC FOR MORE DETAILS. HELENE SHOWS TRUE SYMMETRY...A
DEEP CENTRAL DENSE OVERCAST AND A WELL-DEFINED EYE FEATURE ALL
INDICATIVE OF A MATURE HURRICANE UNDERGOING FLUCTUATIONS IN
INTENSITY. GORDON IN CURRENTLY A CATEGORY TWO HURRICANE ON THE
SAFFIR SIMPSON HURRICANE SCALE...BUT HAS THE POTENTIAL TO REGAIN
A CATEGORY THREE WITH MAXIMUM SUSTAINED WINDS OF 100 KT DURING
THE NEXT 24 HOURS. IT IS NOT EXPECTED TO IMPACT ANY LAND MASS ON
ITS CURRENT FORECASTED TRACK. A BAND OF MODERATE TO STRONG
CONVECTION IS WRAPPING AROUND THE CENTER. THE COLDEST CLOUD TOPS
ARE ON THE WEST SIDE.

...TROPICAL WAVES...
A TROPICAL WAVE IS APPROACHING THE CAPE VERDE ISLANDS. IT AXIS
IS ALONG 21/22W SOUTH OF 21N MOVING WEST AT 10-15 KT. SATELLITE
IMAGERY SHOWS SOME TURNING IN THE CLOUD PATTERN NEAR 13N.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION BETWEEN THE WAVE
AXIS AND THE WEST AFRICAN COAST.

TROPICAL WAVE IS ALONG 40W SOUTH OF 20N MOVING WEST AT 10-15 KT.
WELL-DEFINED INVERTED-V SIGNATURE WITH ASSOCIATED SCATTERED
MODERATE/ISOLATED STRONG CONVECTION E OF THE WAVE AXIS FROM
10N-14N BETWEEN 35W-40W.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 11N15W 9N26W 10N38W 8N42W 6N56W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120-150
NM SOUTH OF THE AXIS E OF 31W TO THE COAST OF AFRICA. A CLUSTER
OF SIMILAR CONVECTION IS WITHIN 200 NM NORTH OF AXIS BETWEEN
49W-52W.

...DISCUSSION...
GULF OF MEXICO...
A DEEP LAYER TROUGH IS MOVING ACROSS THE EASTERN US AND THE
NORTH-CENTRAL GULF WATERS. THE ASSOCIATED FRONTAL SYSTEM EXTENDS
FROM A 1008 MB SURFACE LOW PRES OVER THE CAROLINAS SOUTH-
WESTWARD INTO THE GULF NEAR 30N87W...THEN CONTINUES TO ANOTHER
WEAK SURFACE LOW PRES LOCATED NEAR 26N95W. A PRE-FRONTAL TROUGH
LIES ALONG 31N82W 28N87W. DOPPLER RADAR DEPICTS A SQUALL LINE
MOVING ACROSS NORTHERN FLORIDA AND SCATTERED TO NUMEROUS SHOWERS
AND TSTMS OVER CENTRAL AND SOUTH FLORIDA. THE FRONTAL BOUNDARY
WILL EXTEND FROM NORTH-CENTRAL FLORIDA TO NE MEXICO WEDNESDAY
MORNING AND IS EXPECTED TO CROSS SOUTH FLORIDA DURING THE
AFTERNOON. CONTINENTAL DRY AIR IS ENTERING THE NW PORTION OF THE
GULF...JUST BEHIND THE FRONT. AN UPPER HIGH IS OVER THE BAY OF
CAMPECHE WITH THE UPPER RIDGE EXTENDING NE AHEAD OF THE UPPER
TROUGH. THIS RIDGE COVERS A GOOD PORTION OF THE GULF AND THE
STATE OF FLORIDA. EAST OF THE RIDGE...A BROAD UPPER TROUGH
REMAINS IN THE W ATLC. DIFFLUENCE ALOFT IS ENHANCING THE
SHOWER/TSTM ACTIVITY OVER FLORIDA AND THE ADJACENT COASTAL
WATERS.

THE CARIBBEAN SEA...
THE UPPER TROUGH IN THE W ATLC EXTENDS ACROSS THE BAHAMAS AND
CUBA INTO THE NW CARIBBEAN WITH AN UPPER LOW OVER CENTRAL CUBA.
THE UPPER HIGH THAT IS LOCATED OVER THE BAY OF CAMPECHE ALSO
COVERS SOUTH MEXICO AND CENTRAL AMERICA. A MUCH LARGER UPPER
HIGH REMAINS IN THE E CARIBBEAN AND IS ANCHORED NOW JUST S OF
PUERTO RICO EXTENDING A RIDGE WSW TO 13N80W. THIS FEATURE IS
ADVECTING TROPICAL MOISTURE OVER THE SW CARIBBEAN AND GENERATING
CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION JUST
NORTH OF COLOMBIA AND NEAR LAKE MARACAIBO IN VENEZUELA. SIMILAR
CONVECTION IS SEEN OVER CENTRAL AMERICA DUE TO THE CLOSE
PROXIMITY OF THE ITCZ AND A DIFLUENT PATTERN ALOFT. THE EASTERN
CARIBBEAN REMAINS RATHER DRY...WITH THE TYPICAL AFTERNOON
CONVECTION OVER PUERTO RICO AND HISPANIOLA THANKS TO THE LOCAL
EFFECTS. THE INVERTED TROUGH MENTIONED DURING THE PREVIOUS DAYS
HAS MOVE TO THE SW CORNER OF THE AREA AND IS APPROACHING THE
COAST OF NICARAGUA. TRADE WINDS OF 10-15 KT DOMINATE THE ENTIRE
BASIN.

THE ATLANTIC OCEAN...
BROAD UPPER TROUGH EXTENDS FROM AN UPPER LOW N OF THE REGION
ACROSS THE BAHAMAS AND CUBA. A SURFACE TROUGH RUNS FROM 31N68W
TO 22N77W. SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE WITHIN
AROUND 80 NM EAST OF THE TROUGH. BROAD UPPER HIGH ANCHORED IN
THE E CARIBBEAN EXTENDS A RIDGE NE TO 23N58W JUST W OF HURRICANE
HELENE. THIS SYSTEM IS GIVING THE E CARIBBEAN AND THE W TROPICAL
ATLC VERY DRY AIR. THE UPPER RIDGE ASSOCIATED WITH HURRICANE
HELENE IS ELONGATED N/S. WV IMAGERY SHOWS AN UPPER LOW OVER THE
E ATLC NEAR 23N36W. THIS LOW IS GENERATING ISOLATED SHOWERS
NORTH OF THE AREA. REMAINDER OF THE E ATLC IS DOMINATED BY AN
UPPER HIGH ANCHORED OFF THE COAST OF AFRICA NEAR 17N20W.
ACCORDING TO THE 19/2100 SAHARAN AIR LAYER FROM CIMSS...SOME
AFRICAN DUST IS STILL AFFECTING THE EASTERN
CARIBBEAN...PARTICULARLY THE LESSER ANTILLES.

$$
GR




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