[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 270633
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT WED JUL 27 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 0000 UTC SURFACE ANALYSIS AND
SATELLITE IMAGERY THROUGH 0615 UTC.

...SPECIAL FEATURE...

TROPICAL STORM FRANKLIN CENTER NEAR 32.8N 68.8W AT 27/0600 UTC...
OR ABOUT 240 MILES/390 KM...WEST OF BERMUDA. IT IS MOVING
NORTHWEST 5 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS
1002 MB. THE MAXIMUM SUSTAINED WIND SPEED IS 35 KT GUSTS 45 KT.
SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT1/WTNT21 KNHC AND THE PUBLIC ADVISORY UNDER AWIPS/WMO
HEADERS MIATCPAT1/WTNT31 KNHC FOR MORE DETAILS. FRANKLIN IS
FORECAST TO MOVE NORTHWARD AND THEN NORTHEASTWARD DURING THE
NEXT FEW DAYS. NUMEROUS STRONG SHOWERS AND THUNDERSTORMS FROM
30N TO 32N BETWEEN 67.5W AND 69.5W. THE CLOUD TOP TEMPERATURES
FROM 31N TO 31.5N ARE NEAR -71C AND THE CLOUD TOPS ARE REACHING
52000 FEET. CLOUD TOP TEMPERATURES ELSEWHERE FROM 30N TO 32N
BETWEEN 67W AND 70W ARE CLOSE TO -66C WITH CLOUD TOPS REACHING
48000 FEET.

...TROPICAL WAVES...

EASTERN ATLANTIC OCEAN TROPICAL WAVE ALONG 28W/29W SOUTH OF 17N
MOVING WEST 15 TO 20 KT. LONG-TERM SATELLITE LOOPS...UPPER-AIR
TIMESECTIONS FROM DAKAR AND SAL...AND COMPUTER MODEL DATA
SUGGEST THAT A PERSISTENT AREA OF TSTMS SW OF THE CAPE VERDES
IS A REFLECTION OF A TROPICAL WAVE. THIS WAVE IS SMALLER IN
AMPLITUDE THAN THE ONE IN THE CENTRAL ATLC AND THE ONE SOON TO
EMERGE OFF WEST AFRICA. MOST OF THE SIGNAL OF THE WAVE IS IN
THE MIDDLE LEVELS WITH ONLY A SMALL SURFACE REFLECTION NOTED...
THOUGH THE GFS MODEL SUGGESTS THAT SOME DEVELOPMENT IS POSSIBLE
AS THE SYSTEM MOVES A LITTLE SOUTH OF DUE WEST. IT SEEMS LIKE
EVERY WAVE RECENTLY HAS BEEN A CANDIDATE FOR MORE DEVELOPMENT
WITH THE VERY WARM WATER AND LIGHT VERTICAL SHEAR MORE
REMINISCENT OF THE MIDDLE OF AUGUST RATHER THAN LATE IN JULY.
SCATTERED MODERATE TO ISOLATED STRONG SHOWERS AND THUNDERSTORMS
FROM 9N TO 14N BETWEEN 27W AND 33W.

CENTRAL ATLANTIC OCEAN TROPICAL WAVE IS TILTED FROM NORTHEAST
TO SOUTHWEST ALONG 20N41W TO 14N44W TO 1014 MB LOW CENTER NEAR
11N45W TO 7N46W MOVING WEST 20 KT. THIS WAVE IS MOVING INTO
A PROGRESSIVELY MORE UNSTABLE ATMOSPHERE IN THE WESTERN TROPICAL
ATLANTIC OCEAN. ISOLATED MODERATE SHOWERS AND THUNDERSTORMS FROM
10N TO 17N BETWEEN 41W AND 44W...AND FROM 7N TO 10N BETWEEN 44W
AND 48W. THERE IS STILL PLENTY OF DRY AIR IN THE LARGER WAVE
CIRCULATION BUT THIS SHOULD SLOWLY MIX OUT AS TSTM ACTIVITY
INCREASES. MOISTURE FROM THE WAVE SHOULD ENTER THE LESSER
ANTILLES ON FRIDAY WITH A PRECEDING "TAIL" OF MOISTURE ENTERING
TOMORROW.

CENTRAL CARIBBEAN SEA TROPICAL WAVE ALONG 76W/77W SOUTH OF 18N
MOVING WEST 20 KT. ANY SIGN OF THE WAVE HAS DISAPPEARED IN THE
VERY FAST LOW TO MIDDLE LEVEL FLOW OF THE CENTRAL CARIBBEAN
SEA.  LONG-TERM SATELLITE LOOPS SUGGEST THAT THE WAVE IS RATHER
LOW IN LATITUDE AND COULD BE A COUPLE OF DEGREES MORE TO THE
WEST BUT THE DATA ARE INCONCLUSIVE.  NO SIGNIFICANT SHOWERS.

TROPICAL WAVE MOVING THROUGH THE ISTHMUS OF TEHUANTEPEC OF
MEXICO ALONG 93W SOUTH OF 19N MOVING WEST 10 TO 15 KT.
SHOWERS AND THUNDERSTORMS FROM A FEW HOURS AGO HAVE WEAKENED
IN THE AREA FROM 15N TO 19N BETWEEN 93W AND 97W.

...THE ITCZ...

ITCZ 10N14W 9N20W 13N27W...13N30W 15N36W 15N40W...9N46W 8N50W
10N53W. ELSEWHERE AWAY FROM THE TROPICAL WAVES...SCATTERED
STRONG SHOWERS AND THUNDERSTORMS FROM 8N TO 10N BETWEEN 20W
AND 23W. ISOLATED MODERATE SHOWERS AND THUNDERSTORMS FROM
8N TO 10N BETWEEN 50W AND 54W.

...DISCUSSION...

THE GULF OF MEXICO...
A WEAK SURFACE PRESSURE GRADIENT EXISTS IN THE GULF OF MEXICO.
A SURFACE TROUGH RUNS FROM 27N69W TO AN ATLANTIC 1014 MB LOW
PRESSURE CENTER NEAR 26N75W...THROUGH THE NORTHERN BAHAMAS TO
AN EASTERN GULF OF MEXICO 1013 MB LOW PRESSURE CENTER ALONG THE
FLORIDA WEST COAST NEAR 27N83W...TO 26N87W TO A NORTH CENTRAL
GULF OF MEXICO LOW CENTER NEAR 28N89W. A 1016 MB HIGH PRESSURE
CENTER IS NEAR 24N87W. ISOLATED SHOWERS APPEAR TO BE FROM 26N
TO 29N BETWEEN 86W AND 93W. ONE UPPER LEVEL ANTICYCLONIC
CIRCULATION CENTER IS IN THE NORTHWESTERN GULF...AND ANOTHER ONE
IS OVER THE SOUTHEASTERN UNITED STATES. A NARROW SHEAR AXIS IS
BETWEEN THESE FEATURES FROM NORTHWESTERN CUBA TO SOUTHEASTERN
LOUISIANA. THE UPPER LEVELS ARE DOMINATED BY RELATIVELY DRY AIR
OVER THE AREA. MOISTURE WILL BEGIN TO INCREASE NEAR THE NORTHERN
GULF COAST ON THURSDAY WITH THE APPROACH OF A RARE SUMMERTIME
COLD FRONT...AND MAY TRIGGER SCATTERED THUNDERSTORMS INTO THE
WEEKEND...THOUGH IT IS LIKELY THAT THE FRONT WILL BECOME QUITE
WEAK IF IT EVER ENTERS THE GULF WATERS.

THE CARIBBEAN SEA...
BROAD SURFACE LOW PRESSURE COVERS THE SOUTHWESTERN CORNER OF THE
AREA...FOLLOWING THE SURFACE ISOBARIC PATTERN. ITCZ SHOWERS AND
THUNDERSTORMS ALONG PANAMA COAST...AND WEAKENING BUT REMNANT
ISOLATED MODERATE TO LOCALLY STRONG SHOWERS AND THUNDERSTORMS
STRETCH FROM COSTA RICA TO BELIZE IN THE GULF OF HONDURAS...AND
JUST EAST OF NICARAGUA IN THE WATERS. THE 76W/77W TROPICAL WAVE
IS APPROACHING THIS AREA. AFRICAN DUST AND DRY CONDITIONS ALOFT
COMBINE TO KEEP ALMOST ALL THE THUNDERSTORMS OVER LAND.
THE MID-OCEANIC TROUGH SITS FROM THE SOUTHEASTERN BAHAMAS THROUGH
HAITI TO NORTHEASTERN HONDURAS...TRIGGERING THE SHOWERS IN
CENTRAL AMERICA.

THE WEST AND CENTRAL ATLANTIC OCEAN...
TROPICAL STORM FRANKLIN STILL IS IN THE AREA.
ISOLATED SHOWERS ARE SEEN FROM 24N TO 27N BETWEEN 70W AND
80W...WITH THE SURFACE TROUGH AND 1014 MB SURFACE LOW PRESSURE
CENTER NEAR 26N75W. A SMALL UPPER LOW IS LOCATED JUST SW OF
FRANKLIN NEAR 29N69W AND THE DIFFLUENCE IS HELPING TO
OCCASIONALLY BURST CONVECTION NEAR THE CENTER...WITH PERHAPS
A LITTLE LESS NORTHERLY SHEAR THAN YESTERDAY. A SECOND BUT
DRIER UPPER LOW IS LOCATED NEAR THE TURKS AND CAICOS ISLANDS AND
IS ENHANCING THE NEARLY CLOUD-FREE SKIES OVER THE SRN BAHAMAS.
MORE TO THE EAST A SHARP UPPER LEVEL TROUGH CONTINUES ALONG
30N51W 18N55W AND IS INTERACTING WITH A SFC TROUGH NORTHEAST
OF THE LESSER ANTILLES TO PRODUCE ISOLATED MODERATE CONVECTION
FROM 18N TO 23N BETWEEN 53W AND 63W.

THE EASTERN ATLANTIC OCEAN...
STRONG UPPER LEVEL RIDGING IS ESTABLISHED ALONG 19N AND HAS
INCREASED THE DEEP EASTERLY FLOW OUT OF AFRICA AND ACROSS THE
ATLC WATERS. DRY AIR WITH A BIT OF DUST CONTINUES TO SPREAD OVER
THIS AREA AS WELL AND HAS STABILIZED THE ENVIRONMENT SO THAT
DEEP CONVECTION IS MOSTLY S OF 15N. FARTHER N...A DEEP UPPER
TROF LOCATED W OF PORTUGAL ALONG 16W IS DRIVING A DISSIPATING
COLD FRONT FROM MADEIRA ISLAND TO 28N25W THEN 31N28W WITH ONLY
SCATTERED CLOUDS AND ISOLATED SHOWERS LOCATED ALONG THIS FRONT.
SURFACE RIDGING EXTENDS FROM A 1024 MB HIGH NEAR 30N44W ESE TO
26N16W AND WSW TO 24N65W WITH ANOTHER DAY OF LIGHT TRADES IN THE
DEEP TROPICAL ATLC DUE TO PRESSURES IN THE DEEP TROPICS BEING
HIGHER THAN AVERAGE AND SLIGHTLY BELOW AVERAGE PRESSURES IN THE
CENTRAL ATLC.  VERTICAL WIND SHEAR IS MUCH LESS THAN AVERAGE S
OF 17N E OF THE LESSER ANTILLES.

$$
MT


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