[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 122347
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE 12 OCT 2004

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA... GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN
SECTIONS OF SOUTH AMERICA...AND ATLC 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.

...TROPICAL WAVES...
TROPICAL WAVE ABOUT MIDWAY BETWEEN AFRICA AND THE LESSER
ANTILLES ALONG MEAN AXIS OF 39W S OF 14N MOVING W 10 KT. WAVE
LOOKS SIMILAR TO YESTERDAY WITH A V-SHAPE IN THE LOW/MID CLOUDS
BUT WITH ISOLATED SHOWERS WITHIN 60 NM OF 11N40W.

TROPICAL WAVE NEARING THE ABC ISLANDS ALONG 67W S OF 15N MOVING
W 10 KT. POSITION IS BASED ON EXTRAPOLATION WITH LONG-TERM LOOPS
SUGGESTING THE WAVE HAS BECOME VERY WEAK AND ILL-DEFINED.

...ITCZ...
ITCZ AXIS IS ALONG 10N15W 7N22W 8N45W 10N56W 10N63W.  SCATTERED
MODERATE FROM 4N-7N BETWEEN 22W-28W.  ISOLATED MODERATE FROM
5N-10N BETWEEN 27W-48W AND WITHIN 90 NM OF 4N15W.  WIDELY
SCATTERED WEAK/MODERATE IS FROM 9N-13N BETWEEN 51W-58W...
ASSOCIATED WITH A WEAK SURGE OF MOISTURE THAT SHOULD MOVE ACROSS
THE WINDWARDS TOMORROW.

...DISCUSSION...
GULF OF MEXICO...
RATHER DRY ZONAL FLOW COVERS THE NORTHERN GULF BETWEEN A CUTOFF
LOW OVER MISSOURI AND A STATIONARY MID/UPPER HIGH OVER SE
MEXICO.  THIS ZONAL FLOW IS ALLOWING A COLD FRONT TO SNEAK INTO
THE NW GULF FROM ABOUT NEW ORLEANS TO BROWNSVILLE WITH SLIGHTLY
COOLER/DRIER AIR BEHIND THE FRONT.  HOWEVER IT IS A DRY FRONT
WITH LIMITED MOISTURE AND NO UPPER-AIR SUPPORT.  FARTHER E...
THE REMNANTS OF A COLD FRONT ARE NOW A TROUGH SITTING OVER THE
SUNSHINE STATE THRU NW CUBA INTO THE YUCATAN PENINSULA.  ANY
SIGNIFICANT RAIN HAS PUSHED OFF THE FLORIDA E COAST WITH THE
GULF MOSTLY DEEP CONVECTION-FREE.  STATIONARY HIGH OVER MEXICO
IS LEADING TO PLENTY OF DIURNAL TSTMS OVER CENTRAL AMERICA AND
THE BAY OF CAMPECHE WITH PLENTY OF CIRRUS DEBRIS REMAINING OVER
THE GULF S OF 25N... ALSO FROM T.S. LESTER IN THE EPAC.

CARIBBEAN SEA...
NO SIGNIFICANT CHANGE IN THE NW CARIBBEAN WITH GENERALLY DRY
ANTICYCLONIC FLOW FROM HAITI TO COSTA RICA FROM THE MID/UPPER
HIGH OVER MEXICO.  IN THE E CARIBBEAN...NARROW MID/UPPER TROUGH
RUNS THROUGH THE LEEWARD ISLANDS TO 12N80W WITH WIDELY SCATTERED
TSTMS FROM 11N-14N BETWEEN 79W-82W IN THE SW APEX OF THE
TROUGH.  WIDELY SCATTERED TSTMS HAVE FORMED IN THE GREATER
ANTILLES DUE TO LIGHTER-THAN-AVERAGE UPPER TRADES CONTRIBUTING
TO STRONGER SEA-BREEZES AND HIGH MOISTURE/STEEPER ATMOSPHERIC
LAPSE RATES.  LITTLE CHANGE IS LIKELY OVER THE NE CARIBBEAN BUT
A SURGE IN MOISTURE COULD ENHANCE RAIN CHANCES IN THE WINDWARD
ISLANDS TOMORROW.

SUBTROPICAL ATLC...
W-NW MID/UPPER FLOW BLANKETS THE AREA W OF 55W WITH A COLD FRONT
FROM 31N53W SW TO 24N70W.  WEAK HIGH PRESSURE IS BEHIND THE
FRONT JUST NE OF THE BAHAMAS.  ISOLATED MODERATE FROM 24N-30N
BETWEEN 55W-60W. MID/UPPER LOW IS NEAR 29N50W WITH TROUGH S
TO21N51W AND WSW INTO THE LEEWARD ISLANDS.  DIVERGENCE FROM THE
LOW IS ENHANCING WIDELY SCATTERED MODERATE FROM 24N-28N BETWEEN
46W-49W.  GENTLE UPPER RIDGE AXIS IS ALONG 43W WITH SCATTERED
HIGH CLOUDS DUE TO CIRRUS OUTFLOW FROM UPSTREAM TSTMS.  A LARGE
POWERFUL DEEP-LAYERED LOW IS NEARLY STATIONARY CLOSE TO 31N33W.
THE LOW COULD STILL TRANSITION INTO A SUBTROPICAL OR TROPICAL
CYCLONE BUT CONVECTION IS RATHER ASYMMETRIC ON THE E SIDE OF THE
CIRCULATION WITH WIDELY SCATTERED MODERATE FROM 28N-32N BETWEEN
26W-33W.  ASSOCIATED COLD FRONT ENTERS THE E ATLC NEAR 31N21W TO
26N23W SW TO 22N30W WEAKENING TO 22N41W.  ISOLATED MODERATE
WITHIN 75 NM OF 30N20W WITH A LARGE AREA OF OVERCAST CLOUDS AND
WIDELY SCATTERED SHOWERS ARE N OF 20N W OF THE CANARY ISLANDS TO
25W. WIDELY SCATTERED SHOWERS ARE FROM 23N-27N BETWEEN 24W-31W.

TROPICAL ATLC...
OTHER THAN A NARROW TROUGH OVER THE EXTREME NW PART OF THE
AREA... GENERALLY A FLAT RIDGE COVERS THE WESTERN DEEP TROPICS
WITH RIDGE AXIS ALONG 11N FROM THE WINDWARDS TO 35W AND
GENERALLY DRY CONDITIONS SAVE SOME ITCZ ACTIVITY.  IN THE E
ATLC... TROUGHING FROM THE DEEP NE ATLC LOW ENTERS THE AREA NEAR
20N30W SSW TO 9N34W.  THE SOUTHERN EDGE OF THE TROUGH IS
ENHANCING ITCZ CONVECTION OTHERWISE MODERATE MID/UPPER
SUBSIDENCE IS PRESENT.

$$
BLAKE

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