[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 181833
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON SEP 18 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...SPECIAL FEATURES...
THE CENTER OF HURRICANE HELENE AT 18/1500 UTC WAS NEAR
23.2N 50.2W. HELENE IS MOVING NORTHWEST 8 KT. THE ESTIMATED
MINIMUM CENTRAL PRESSURE IS 954 MB. THE MAXIMUM SUSTAINED WIND
SPEEDS ARE 110 KT WITH GUSTS TO 135 KT. HELENE IS A CATEGORY
THREE HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE.
PLEASE READ THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO
HEADERS MIATCMAT3/WTNT23 KNHC OR THE PUBLIC ADVISORY UNDER
MIATCPAT3/ WTNT33 KNHC FOR MORE DETAILS. NUMEROUS STRONG SHOWERS
AND THUNDERSTORMS ARE WITHIN A 90 NM RADIUS OF THE CENTER. THE
COLDEST CLOUD TOP TEMPERATURES ARE NEAR -80C WITHIN 50 NM OF THE
CENTER NORTHWEST THROUGH NORTH. OVERCAST HIGH LEVEL CLOUDS COVER
THE WATERS TO THE NORTH OF HELENE TO 30N BETWEEN 46W AND 53W.

THE CENTER OF HURRICANE GORDON AT 18/1500 UTC WAS NEAR
37.3N 47.6W. GORDON IS MOVING NORTHEAST 17 KT. THE ESTIMATED
MINIMUM CENTRAL PRESSURE IS 980 MB. THE MAXIMUM SUSTAINED WIND
SPEEDS ARE 80 KT WITH GUSTS TO 100 KT. PLEASE READ THE LATEST
NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22
KNHC OR THE PUBLIC ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE
DETAILS. NUMEROUS STRONG SHOWERS AND THUNDERSTORMS ARE WITHIN
A 50 NM RADIUS OF THE CENTER.

...TROPICAL WAVES...
AN EASTERN ATLANTIC OCEAN TROUGH IS ALONG 28W FROM 18N TO 24N.
THIS TROUGH IS THE REMNANT OF THE FORMER SURFACE LOW PRESSURE
CENTER NEAR 18N22W FROM 24 HOURS AGO. THE LOW CENTER HAS BECOME
DISORGANIZED AND BECOME THE PRESENT TROUGH.

AN EASTERN ATLANTIC OCEAN TROPICAL WAVE IS ALONG 36W AT
18/1745 UTC ACCORDING TO CURRENT VISIBLE SATELLITE IMAGERY.
THIS SCENARIO IS NOT WHAT WE HAVE DEPICTED IN THE 18/1200 UTC
SURFACE MAP ANALYSIS. WE PUT A TROPICAL WAVE AT 28W. WE HAVE
REASONED NOW THAT WHAT IS AT 28W IS A TROUGH...AND THAT THE
WAVE ACTUALLY IS ALONG 35W. ISOLATED MODERATE SHOWERS AND
POSSIBLE THUNDERSTORMS FROM 9N TO 13N BETWEEN 33W AND 38W.
LOW TO MIDDLE LEVEL CLOUDS ARE MOVING WITH THIS WAVE.

ISOLATED MODERATE SHOWERS AND POSSIBLE THUNDERSTORMS ARE IN
A LINE ALONG THE ITCZ AXIS WHICH CURVES NORTHWARD TOWARD
HURRICANE HELENE. THE PRECIPITATION IS FROM 6N TO 19N BETWEEN
40W AND 50W.

THE TROPICAL WAVE THAT WAS MOVING THROUGH THE YUCATAN PENINSULA
SIX HOURS AGO HAS BEEN DROPPED FROM THE SURFACE MAP ANALYSIS
BECAUSE OF LACK OF DATA IN ORDER TO PROVE ITS EXISTENCE.

...THE ITCZ...
8N12W 7N30W 8N38W CURVING NORTHWARD TO 16N43W...FROM 16N46W
CURVING TO 12N50W 10N57W 10N63W. ISOLATED MODERATE SHOWERS AND
LOCALLY STRONG THUNDERSTORMS ARE IN CLUSTERS...ALONG THE AFRICA
COAST FROM 8N TO 11N BETWEEN 13W AND 14W...FROM 9N TO 10N
BETWEEN 17W AND 19W...AND FROM 5N TO 10N BETWEEN 18W AND 33W.
ISOLATED MODERATE SHOWERS AND POSSIBLE THUNDERSTORMS ARE IN
A LINE ALONG THE ITCZ AXIS WHICH CURVES NORTHWARD TOWARD
HURRICANE HELENE. THE PRECIPITATION IS FROM 6N TO 19N
BETWEEN 40W AND 50W.

...DISCUSSION...

THE GULF OF MEXICO AND THE WESTERN ATLANTIC OCEAN
NORTHWEST OF THE LINE FROM 32N60W TO THE SOUTHERN BAHAMAS...
A DEEP LAYER TROUGH IS MOVING THROUGH TEXAS AT THIS TIME.
THE TROUGH ON WATER VAPOR IMAGERY PASSES THROUGH EASTERN
OKLAHOMA TO CENTRAL TEXAS TO NORTHERN MEXICO NEAR 27N102W.
A SURFACE COLD FRONT RUNS FROM NORTHEASTERN TEXAS TO SOUTH
CENTRAL TEXAS TO THE TEXAS BIG BEND TO THE FAR WEST TEXAS.
THE STRONGEST SHOWERS AND THUNDERSTORMS COVER THE DEEP SOUTH
OF TEXAS INTO NORTHEASTERN MEXICO FROM 24N TO 27N BETWEEN
97W AND 100W. OVERCAST HIGH CLOUDS ARE CURVING ANTICYCLONICALLY
TO THE NORTH AND NORTHWEST OF 22N98W 25N90W 30N88W. ISOLATED
TO WIDELY SCATTERED MODERATE TO STRONG SHOWERS AND THUNDERSTORMS
FROM MISSISSIPPI TO SOUTHEASTERN LOUISIANA FROM 29N TO 31N
BETWEEN 90W AND 92W. A DEEP LAYER TROUGH IS ALONG THE U.S.A.
EAST COAST. A TROUGH THAT APPEARS IN THE WATER VAPOR IMAGERY
GOES FROM A LOW PRESSURE CENTER NEAR 34N70W TO 31N76W TO 24N81W.
ISOLATED MODERATE SHOWERS AND LOCALLY STRONG THUNDERSTORMS ARE
WITHIN 30 TO 60 NM ON EITHER SIDE OF 24N73W 23N78W 25N82W
26N84W...AND FROM THE WATERS JUST OFF THE FLORIDA PANHANDLE INTO
SOUTHEASTERN ALABAMA. THIS PRECIPITATION IS IN THE AREA OF
DIFFLUENT UPPER LEVEL WIND FLOW...DIFFLUENT WITH RESPECT TO THE
U.S.A. EAST COAST TROUGH AND THE UPPER LEVEL RIDGE THAT IS IN
BETWEEN THE EAST COAST TROUGH AND THE TEXAS TROUGH. A SURFACE
TROUGH PASSES THROUGH 32N65W TO 27N70W TO 24N81W. SHOWERS AND
THUNDERSTORMS FROM FROM THE WATERS JUST OFF THE SOUTHWESTERN
COAST OF FLORIDA...THROUGH THE STRAITS OF FLORIDA TO THE BAHAMAS
FROM 22N TO 25N...FROM 22N TO 27N BETWEEN 70W AND THE BAHAMAS...
AND THEN WITHIN 30 NM ON EITHER SIDE OF 31N60W 28N61W. ISOLATED
MODERATE SHOWERS ELSEWHERE FROM 23N TO 29N BETWEEN 60W AND 70W.
MIDDLE LEVEL DRY AIR COVERS PRETTY MUCH ALL THE GULF WATERS
EXCEPT FOR THE SOUTHWESTERN CORNER. HIGH CLOUDS FROM SOME
CONVECTIVE PRECIPITATION AT THE WESTERN EDGE OF THE GULF OF
TEHUANTEPEC IS CURVING ANTICYCLONICALLY INTO THE SOUTHWESTERN
CORNER OF THE GULF OF MEXICO. A MIDDLE LEVEL LOW PRESSURE CENTER
IS SPINNING AROUND IN THE DRY AIR NEAR 22N97W A LITTLE BIT EAST
OF TAMPICO MEXICO.

THE CARIBBEAN SEA...
BROAD UPPER LEVEL ANTICYCLONIC FLOW COVERS SOUTHERN MEXICO
IN THE AREA OF THE ISTHMUS OF TEHUANTEPEC AND EASTWARD TO
GUATEMALA. THE BASE OF THE DEEP ATLANTIC OCEAN/EASTERN U.S.A.
COAST TROUGH REACHES THE NORTHWESTERN CORNER OF THE AREA...ABOUT
120 NM SOUTH OF WESTERN CUBA. AN INVERTED MIDDLE TO UPPER LEVEL
TROUGH AND ITS ASSOCIATED CYCLONIC FLOW STILL COVER THE
SOUTHWESTERN CORNER OF THE AREA. THE SHOWERS AND THUNDERSTORMS
IN THE WATERS OFF THE NORTHERN COAST OF COLOMBIA ARE IN AN AREA
OF UPPER LEVEL DIFFLUENT FLOW...AS SOME OF THE FLOW VEERS AWAY
FROM THE INVERTED TROUGH TOWARD THE CENTRAL CARIBBEAN SEA.
ISOLATED MODERATE SHOWERS COVER THE SOUTHWESTERN WATERS WEST OF
80W SOUTH OF 15N AND EVEN INTO NORTHEASTERN NICARAGUA AND EXTREME
SOUTHEASTERN HONDURAS...IN THE AREA OF THE INVERTED TROUGH.
BROAD UPPER LEVEL ANTICYCLONIC FLOW AND DRY AIR ARE EAST OF 70W.
A BIT OF THE DEEP LAYER ATLANTIC OCEAN TROUGH WHOSE BASE IS JUST
SOUTH OF CUBA SEEPS INTO THE NORTH CENTRAL WATERS IN BETWEEN
HAITI...CUBA...AND JAMAICA.

THE ATLANTIC OCEAN...
BROAD UPPER LEVEL ANTICYCLONIC FLOW AND DRY AIR COVER THE
ATLANTIC OCEAN AND THE CARIBBEAN SEA FROM 10N TO 27N BETWEEN
55W AND 70W...RIGHT UP TO THE FLOW AROUND HURRICANE HELENE.
AN EASTERN ATLANTIC OCEAN TROUGH RUNS FROM 26N28W TO A LOW
PRESSURE CENTER NEAR 20N31W 13N36W...NEAR WHERE THE 36W
TROPICAL WAVE IS PASSING UNDERNEATH IT. BROAD UPPER LEVEL
ANTICYCLONIC FLOW COVERS THE REST OF THE ATLANTIC OCEAN WATERS
EAST OF THE 26N28W 13N36W TROUGH. SCATTERED STRONG SHOWERS AND
THUNDERSTORMS FROM 21N TO 22N BETWEEN 26W AND 28W.


$$
MT



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