Prognostic Meteorological Discussion
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 PM EDT FRI JUL 21 2017

AT 15 UTC TROPICAL DEPRESSION NINE-E CENTERED NEAR 09N
93.5W...WITH MINIMAL CENTRAL PRESSURE OF 1008 HPA AND MAXIMUM
SUSTAINED WINDS OF 30KT. THE DEPRESSION IS MOVING WEST AT 12KT.
SEE NHC DISCUSSION FOR OFFICIAL FORECAST.

TROPICAL DISCUSSION FROM JUL 21/12 UTC: AT 500/250 HPA A RIDGE
EXTENDS WEST TO EAST ACROSS THE CENTRAL TO THE MID ATLANTIC REGION
OF THE USA. A HIGHER AMPLITUDE MID LEVEL RIDGE LIES TO THE
EAST...ENVELOPING THE WESTERN ATLANTIC-NORTHERN CARIBBEAN ISLES. A
TROUGH OVER THE SOUTHEAST USA SEPARATES THESE RIDGES WHILE
CENTERING ON A CLOSED LOW OVER NORTHERN FLORIDA. A MID LEVEL LOW
OVER NORTHERN FLORIDA ANCHORS THIS TROUGH. UNDER INFLUENCE OF THE
RIDGE OVER THE USA THE TROUGH IS TO MEANDER WEST ALONG THE GULF
COAST OF THE USA TO TEXAS/NORTHWEST GULF LATER ON SATURDAY/EARLY
SUNDAY MORNING...WHERE IT IS TO THEN REMAIN THROUGH MONDAY
MORNING. EARLY IN THE CYCLE TIS IS TO ENHANCE CONVECTIVE
INSTABILITY WHILE VENTING DEEP CONVECTION ACROSS THE NORTHWEST
BAHAMAS. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY
AND MAXIMA OF 15-30MM. ON SATURDAY...AS THE TROUGH PULLS
AWAY...THIS WILL DECREASE TO 05-10MM/DAY AND MAXIMA OF 15MM. ON
SUNDAY IT DECREASES TO 00-05MM/DAY WITH WIDELY ISOLATED MAXIMA OF
10MM ACROSS ANDROS ISLAND.

THE MID LEVEL RIDGE OVER THE WESTERN ATLANTIC IS TO CENTER ON A
CLOSED HIGH THAT IS TO MEANDER JUST SOUTH OF BERMUDA DURING THE
NEXT FEW DAYS. THIS IS TO REMAIN THE DOMINANT FEATURE ACROSS THE
GREATER ANTILLES THROUGH MONDAY...MEANWHILE FAVORING AN ELEVATED
INVERSION ACROSS THE NORTHERN CARIBBEAN ISLANDS THAT IS TO
CONTINUE INHIBITING ORGANIZED DEEP CONVECTION. AT UPPER LEVELS...A
TUTT LOW CENTERS TO THE NORTH OF THE TURKS AND CAICOS ISLANDS.
SINCE IT LIMITS TO UPPER ATMOSPHERE THIS WILL NOT BE ABLE TO
OVERCOME NEGATIVE INFLUENCE OF MID LEVEL RIDGE PATTERN. AS A
RESULT...SHALLOW CONVECTION IS TO PREVAIL ACROSS THE
NORTHERN-NORTHEAST CARIBBEAN ISLES DURING THE NEXT FEW DAYS. IN
SHALLOW CONVECTION EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND
MAXIMA OF 10MM FROM EASTERN CUBA-JAMAICA TO THE LEEWARD ISLES.
THROUGH SUNDAY MORNING ACTIVITY IS TO INTENSIFY ACROSS THE EASTERN
CARIBBEAN ISLES AS A STRONGER TROPICAL WAVE ENTERS THE
BASIN....WITH CONVECTION ACROSS PUERTO RICO-HISPANIOLA-VIRGIN
ISLES/LEEWARD ISLANDS INCREASING TO 05-10MM/DAY AND MAXIMA OF
15-30MM.

AS THE MID/UPPER LEVEL TROUGH RETROGRESSES ACROSS THE NORTHERN
GULF TO TEXAS ON SATURDAY IT IS TO THEN ABSORB THE REMNANTS OF A
TUTT OVER THE WESTERN GULF/CENTRAL MEXICO. ON SATURDAY THESE
COMBINE INTO A BROAD TROUGH ACROSS MEXICO. EARLY IN THE CYCLE THIS
IS TO FAVOR AN INCREASE IN CONVECTION ACROSS THE SOUTHERN STATES
OF OAXACA-CHIAPAS...WHERE IT IS TO RESULT IN RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-30MM. THROUGH SUNDAY THIS DECREASES
TO 05-10MM/DAY AND MAXIMA OF 15-20MM WHILE BUILDING WEST ACROSS
CENTRAL MEXICO. OVER NORTHEAST MEXICO EXPECTING RAINFALL AMOUNTS
OF 00-05MM/DAY AND MAXIMA OF 10MM...CLUSTERING BETWEEN EASTERN
CHIHUAHUA-COAHUILA TO NORTHERN VERACRUZ. OVER MEXICO/MEXICO-DF AND
SOUTHWEST MEXICO EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-25MM/DAY THROUGH SUNDAY MORNING...WITH MAXIMA THEN
DECREASING TO 15-20MM. HIGHER AMOUNTS ARE TO CLUSTER ALONG THE
SIERRA MADRE OCCIDENTAL...WITH CONVECTION ACROSS SONORA/WESTERN
CHIHUAHUA TO FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF
20-35MM/DAY.

FARTHER SOUTH...AT 250 HPA...THE SUBEQUATORIAL RIDGE EXTENDS
ACROSS THE TROPICAL ATLANTIC-CARIBBEAN BASIN TO CENTRAL AMERICA.
AS THE UPPER LEVEL TROUGH OVER THE GULF BECOMES BETTER ORGANIZED
ON SATURDAY...THE SUBEQUATORIAL RIDGE IS TO THEN GRADUALLY BUILD
ACROSS THE WESTERN CARIBBEAN-EASTERN TROPICAL PACIFIC DURING THE
WEEKEND. THE RIDGE ALOFT IS TO VENT DEEP CONVECTION ALONG THE
ITCZ-NEAR EQUATORIAL TROUGH OVER SOUTHERN CENTRAL AMERICA-NORTHERN
SOUTH AMERICA. OVER HONDURAS-EL SALVADOR-NICARAGUA EXPECTING
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM....WITH
LOCALLY HIGHER IN ASSOCIATION WITH TROPICAL WAVES. ACROSS
PANAMA-COSTA RICA INITIALLY EXPECTING RAINFALL AMOUNTS OF
15-20MM/DAY AND MAXIMA OF 25-50MM. THROUGH SUNDAY THIS WILL
DECREASE TO 05-10MM/DAY AND MAXIMA OF 15-20MM. ON THE WESTERN
PLAINS OF COLOMBIA/ANDEAN REGION EXPECTING RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-25MM/DAY. OVER NORTHERN
COLOMBIA-EASTERN PLAINS AND NORTHWEST VENEZUELA EXPECTING RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM/DAY. HIGHER AMOUNTS
ARE EXPECTED TO THE EAST OVER VENEZUELA...WITH RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-40MM/DAY. ON SATURDAY...UNDER
INFLUENCE OF A TROPICAL WAVE...THE MAXIMA INCREASES TO 30-60MM.
OVER THE GUIANAS SEA BREEZE/DIURNAL CONVECTION IS TO FAVOR
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM...WITH MOST
ACTIVE ALONG THE COAST.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL   24     36     48     60     72     84     96     TYPE
56W      59W    62W    64W    66W    69W    72W    75W     TW
66W      69W    73W    77W    81W    84W    88W    91W     EW
83W      87W    90W    93W    DISSIPATES                   TW
91W      94W    97W    99W   100W   DISSIPATES             TWS
107W    111W   113W   114W   115W   117W   118W   119W     TW

A TROPICAL WAVE ALONG 51W AND SOUTH OF 23N IS TO TRIGGER SCATTERED
CONVECTION ACROSS NORTHERN GUYANA...WITH ACCUMULATION OF
05-10MM/DAY AND MAXIMA OF 15-20MM THROUGH THIS EVENING. OVER
EASTERN VENEZUELA IT IS TO INITIALLY FAVOR RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-40MM. ON SATURDAY THIS INCREASES TO
15-20MM/DAY AND MAXIMA OF 30-60MM AS IT INTERACTS WITH THE NEAR
EQUATORIAL TROUGH. OVER THE WINDWARD ISLES-TRINIDAD/TOBAGO AND
NORTH COAST OF VENEZUELA THIS IS TO THEN FAVOR RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15MM...WHILE OVER THE LEEWARD
ISLES-PUERTO RICO EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-30MM. ON SUNDAY...LOCALIZED MAXIMA OVER WESTERN
PUERTO RICO COULD PEAK AT 75-125MM. OVER NORTHWEST VENEZUELA-ABC
ISLES THIS IS TO THEN TRIGGER RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15MM ON SUNDAY...WHILE OVER HISPANIOLA EXPECTING
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM.

AN EASTERLY WAVE ALONG 66W AND SOUTH OF 19N TRIGGER SCATTERED
CONVECTION ACROSS EASTERN PORTIONS OF PUERTO RICO AND THE SAN JUAN
METRO AREA. AS IT PULLS ACROSS HISPANIOLA THIS IS TO TRIGGER
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM...WHILE OVER
NORTHWEST VENEZUELA-NORTHERN COLOMBIA THE MAXIMA IS TO PEAK AT
15-25MM. OVER EASTERN CUBA-JAMAICA THIS IS TO TRIGGER RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM ON SATURDAY-SUNDAY...AND
OVER WESTERN COLOMBIA-THE DARIEN IN EASTERN PANAMA IT IS TO
SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM ON
SATURDAY. OVER WESTERN PANAMA-COSTA RICA INITIALLY EXPECTING
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM. THROUGH
SUNDAY THIS DECREASES TO 05-10MM/DAY AND MAXIMA OF 15-20MM.
SIMILAR AMOUNTS ARE EXPECTED ACROSS CENTRAL/SOUTHERN NICARAGUA ON
SUNDAY...WHILE OVER NORTHEAST NICARAGUA/NORTHEAST HONDURAS
EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM.

A TROPICAL WAVE ALONG 83W AND SOUTH OF 18N IS FORECAST TO
DISSIPATE EARLY ON SUNDAY. MEANWHILE...OVER EL SALVADOR/WESTERN
HONDURAS TO GUATEMALA THIS IS TO SUSTAIN RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-30MM. OVER BELIZE-NORTHERN GUATEMALA
IT IS TO TRIGGER RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF
10MM. ON SATURDAY...ON THE SOUTHERN STATES OF MEXICO...EXPECTING
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM.

THE LEADING EDGE OF A TRADE WINDS SURGE IS INITIALIZED ALONG 91W.
THIS IS TO GRADUALLY BECOME ILL ORGANIZED EARLY ON SUNDAY.
MEANWHILE...AS IT PULLS ACROSS CENTRAL MEXICO THIS IS TO TRIGGER
SCATTERED CONVECTION WITH ACCUMULATION OF 05-10MM/DAY AND MAXIMA
OF 15-25MM...WHILE ON THE NORTHEAST STATES OF MEXICO EXPECTING
RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM.

A TROPICAL WAVE ALONG 107W AND SOUTH OF 19N IS TO CONFINE TO THE
EASTERN PACIFIC ITCZ.

GAJADHAR...SLMS (SAINT LUCIA)
DAVISON...WPC (USA)
$$





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