[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 170603
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT SUN SEP 17 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0530 UTC.

...SPECIAL FEATURES...
HURRICANE GORDON WAS CENTERED NEAR 32.0N 53.9W OR ABOUT 560 NM
EAST OF BERMUDA AT 17/0300 UTC AND IS MOVING NORTH NEAR 3 KT.
THIS GENERAL MOTION WITH A GRADUAL INCREASE IN FORWARD SPEED IS
EXPECTED DURING THE NEXT 24 HOURS. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 987 MB. MAXIMUM SUSTAINED WINDS ARE 65 KT WITH GUSTS
TO 80 KT. SLOW WEAKENING IS FORECAST DURING THE NEXT 24
HOURS...AND GORDON IS EXPECTED TO BECOME A TROPICAL STORM ON
SUNDAY. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO
HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. SCATTERED
MODERATE CONVECTION ASSOCIATED WITH GORDON LIES FROM 31N-35N
BETWEEN 51W-56W.

 HURRICANE HELENE WAS CENTERED NEAR 19.5N 47.5W OR ABOUT 890 NM
EAST OF THE NORTHERN LEEWARD ISLANDS AT 17/0300 MOVING
WEST-NORTHWEST AT 9 KT. A MOTION BETWEEN WEST-NORTHWEST AND
NORTHWEST IS EXPECTED DURING THE NEXT 24 HOURS. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 984 MB. MAXIMUM SUSTAINED WIND SPEED
IS 70 KT WITH GUSTS TO 85 KT. SLOW STRENGTHENING IS FORECAST
DURING THE NEXT 24 HOURS. SEE THE LATEST NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS.
NUMEROUS MODERATE/ISOLATED STRONG CONVECTION ASSOCIATED WITH
HELENE LIES FROM 18N-23N BETWEEN 45W-50W.

...TROPICAL WAVES...

A BROAD 1012MB LOW NEAR 16N23W...MOVING WNW NEAR 10 KT...IS
APPROACHING THE EASTERN CAPE VERDE ISLANDS BUT STILL REMAINS
ABSENT OF SIGNIFICANT CONVECTION. THIS LOW MAY BE TRANSITIONING
BACK INTO AN OPEN WAVE BUT SHORTWAVE IR IMAGERY STILL SHOWS
CYCLONIC ROTATION OF THE LOW CLOUD FIELD ABOUT A FIXED POINT SO
HAVE KEPT THE LOW. SHOWER ACTIVITY CONTINUES TO DECREASE...AND
NO SIGNIFICANT DEVELOPMENT IS EXPECTED AS THE SYSTEM MOVES OVER
COOLER WATERS.

A WESTERN CARIBBEAN TROPICAL WAVE IS ALONG 80W S OF 18N MOVING W
10 TO 15 KT. SLIGHT VEERING OF THE WINDS AT BUOY 42057 SUGGEST
THE WAVE AXIS HAS RECENTLY PASSED...AND THUS HAVE PLACED THE
AXIS JUST IN LEE OF THIS BUOY ON THE 2100 UTC MAP. CLUSTERS OF
SCATTERED MODERATE CONVECTION ASSOCIATED WITH THIS WAVE ARE SEEN
APPROACHING NICARAGUA/HONDURAS FROM 12N-16N BETWEEN
80W-84W...AND ALSO IN THE NW CARIB FROM 17N-20N BETWEEN 78W-86W.

TROPICAL WAVE IS OVER CENTRAL AMERICA ALONG 88W/89W S OF 17N
MOVING W NEAR 10 KT. CYCLONIC TURNING OF THE LOW TO MID CLOUD
FIELD IS BEST SEEN IN THE EPAC WATERS OFF CENTRAL
AMERICA...THOUGH THE AVAILABLE SFC OBSERVATIONS OVER CENTRAL
AMERICA AND SE MEXICO ALSO SUGGEST CYCLONIC TURNING ABOUT THE
WAVE AXIS. PATCHES OF SCATTERED MODERATE CONVECTION ARE FROM
11N-17N BETWEEN 87W-93W.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 8N13W 9N37W 16N43W 15N49W TO INLAND
OVER SOUTH AMERICA NEAR 9N61W...REEMERGING INTO THE SRN
CARIBBEAN AND TO THE COAST OF PANAMA NEAR 9N78W. A SMALL CLUSTER
OF SCATTERED MODERATE CONVECTION RECENTLY MOVED OFF THE COAST OF
SIERRA LEONE FROM 6N-8N BETWEEN 13W-16W. ISOLATED SHOWERS/TSTMS
ARE WITHIN 100NM OF EITHER SIDE OF THE AXIS BETWEEN 24W-43W.

...DISCUSSION...

GULF OF MEXICO...
LITTLE SIGNIFICANT WEATHER IS AFFECTING THE GULF TONIGHT...WITH
ABUNDANT DRY MID TO UPPER LEVEL AIR HOVERING OVER THE AREA.
THERE ARE A FEW ISOLATED SHOWERS IN THE MIDDLE GULF WATERS FROM
22N-28N BETWEEN 86W-93W...ASSOCIATED WITH UPPER DIFFLUENT AIR
BETWEEN THE FLOW AROUND AN UPPER ANTICYCLONE OVER MEXICO AND THE
TROUGHING OFF THE U.S. EAST COAST. THESE SMALL CELLS ARE BARELY
ABLE TO SUSTAIN THEMSELVES IN THE MIDST OF THE DRY AIR PRESENT.
FAIRLY LIGHT 5-15 KT ANTICYCLONIC SE/S FLOW DOMINATES AT THE
SURFACE TONIGHT. THE EXCEPTION IS 15-20KT SE/S FLOW IN THE
W/NW PORTION WHERE A SLIGHTLY STRONGER GRADIENT IS IN TACT AS
THE WRN PORTION OF HIGH PRESSURE INTERACTS WITH LOWER PRESSURE
OVER MEXICO.

CARIBBEAN SEA...
TWO TROPICAL WAVES ARE TRAVERSING THE CARIBBEAN SEA PRODUCING
CONVECTION W OF 78W AS DESCRIBED ABOVE. MUCH OF THE CARIBBEAN E
OF 78W IS DOMINATED BY DRY MID TO UPPER LEVEL AIR AND FAIR
WEATHER. THE UW-CIMMS SAHARAN AIR LAYER ANALYSIS ALSO SUGGESTS
THIS AREA IS UNDER THE INFLUENCE OF DENSE SAHARAN DUST. A MID TO
UPPER LEVEL HIGH IS OVER THE WRN CARIBBEAN...WITH AN ESTIMATED
CENTER NEAR 17N79W. THERE IS A MID TO UPPER LEVEL TROUGH AXIS
THAT EXTENDS NORTH FROM VENEZUELA AND INTO THE CARIBBEAN MORE OR
LESS ALONG 68W TO NEAR THE MONA PASSAGE...BUT DRY AIR IS
INHIBITING CONVECTION. AT THE SURFACE...10-20KT TRADES DOMINATE
EXCEPT SLIGHTLY STRONGER JUST N OF THE COLOMBIAN COAST.

ATLANTIC OCEAN...
PRONOUNCED DEEP LAYER TROUGHING OFF THE US EAST COAST IS
ANCHORED BY AN UPPER LOW ABOUT 150NM E OF KITTY HAWK NC.
ASSOCIATED SLOW MOVING COLD FRONT IS OVER THE W ATLC ALONG
32N69W 25N80W.  DOPPLER RADAR AND IR SATELLITE IMAGERY SUGGESTS
THE MOST SIGNIFICANT CONVECTION ASSOCIATED WITH THIS FRONT NOW
OVER THE FLORIDA STRAITS...ELSEWHERE ISOLATED SHOWERS/TSTMS ARE
WITHIN 75NM OF THE FRONTAL BOUNDARY. A MID TO UPPER LEVEL HIGH
IS NNE OF THE LEEWARD ISLANDS NEAR 23N62W. OUTFLOW IS SEEN IN
SATELLITE IMAGERY OVER THE CENTRAL ATLC HURRICANES GORDON AND
HELENE...WITH GOES HIGH DENSITY WINDS ALSO DEPICTING THIS WELL.
A MID TO UPPER LEVEL TROUGH IS OVER THE ERN ATLC ALONG 20N33W
32N26W. UPPER DIFFLUENT AIR BETWEEN THIS FEATURE AND THE UPPER
HIGH OVER WRN AFRICA IS HELPING TO SUPPORT THE SCATTERED
SHOWERS/TSTMS FROM 18N-29N BETWEEN 16W-24W. ELSEWHERE AT THE
SURFACE...A 1018MB HIGH IS CENTERED NEAR 25N63W...WITH A 1024MB
HIGH N OF THE AREA NEAR 34N37W...A 1023MB HIGH CENTER FURTHER E
NEAR 35N18W.

$$
WILLIS





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