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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1943Z Dec 06, 2017)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
243 PM EST WED DEC 06 2017

TROPICAL DISCUSSION FROM DEC 06/12 UTC: DEEPENING POLAR TROUGH
OVER THE USA REMAINS THE SYSTEM OF CONCERN. CONSISTENT WITH
PREVIOUS FORECAST...ON THURSDAY THE TROUGH IS TO DEEPEN ACROSS THE
CENTRAL USA WHILE TRAILING ACROSS TEXAS TO THE NORTHERN STATES OF
MEXICO. ON FRIDAY-SATURDAY IT PUSHES FARTHER EAST AND SOUTH INTO
THE GULF AND THE NORTHERN STATES OF MEXICO. AT LOW LEVELS THE
TROUGH ALOFT SUSTAINS A SURFACE FRONT ACROSS THE NORTHERN GULF TO
THE NORTHERN STATES OF MEXICO. THE FRONT IS TO REMAIN NEARLY
STATIONARY THROUGH THURSDAY MORNING. LATER IN THE DAY...UNDER
INFLUENCE OF 25-30KT WIND SURGE OVER THE WESTERN GULF...THE FRONT
MOVES SOUTH ACROSS TAMAULIPAS TO VERACRUZ. ON FRIDAY MORNING THE
WINDS INCREASE TO 35-40KT...WITH THE FRONT MOVING SOUTH TO THE
YUCATAN-SOUTHERN MEXICO LATER IN THE DAY. THE ENSUING
TEHUANTEPECER JET IS TO PEAK AT 45-50KT. ON SATURDAY MORNING THE
FRONT MOVES TO GRAND BAHAMA...WHILE TRAILING ACROSS WESTERN CUBA
TO THE GULF OF HONDURAS. STRONG LOW LEVEL NORTHERLIES OVER THE
WESTERN CARIBBEAN ARE FORECAST TO PEAK AT 35-40KT. THIS WILL
COMBINE WITH A COLD ADVECTIVE PATTERN TO SUSTAIN HEAVY CONVECTION
ALONG THE NORTH COAST OF HONDURAS/ISLAS DE LA BAHIA. LATER ON
SATURDAY THE FRONT WILL MOVE TO THE CENTRAL BAHAMAS-CENTRAL
CUBA-CAYMAN ISLES TO NORTHEAST HONDURAS/ NICARAGUA.

AS IT MEANDERS OVER THE NORTHERN STATES OF MEXICO THE FRONT IS TO
FAVOR MODERATE RAINFALL AMOUNTS ACROSS COAHUILA-NORTHERN
CHIHUAHUA...WITH RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF
20-35MM. ON THURSDAY SOLID PRECIPITATION WILL PREVAIL...WITH
SNOWFALL AMOUNTS OF 15-20CM AND MAXIMA OF 25-50CM ACROSS
COAHUILA/PARTS OF NUEVO LEON. LIGHTER SNOWFALL ACCUMULATIONS ARE
EXPECTED IN CHIHUAHUA. ACROSS THE STATE OF VERACRUZ MOST ACTIVE IS
EXPECTED TO THE SOUTH...TO ALSO AFFECT NORTHERN PORTIONS OF
CHIAPAS ON WEDNESDAY TO FRIDAY WHERE IT IS TO FAVOR RAINFALL
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM/DAY. OVER THE
NORTHWEST BAHAMAS EXPECTING RAINFALL AMOUNTS 10-15MM/DAY AND
MAXIMA OF 20-35MM ON FRIDAY-SATURDAY...WHILE OVER WESTERN CUBA
THIS IS TO TRIGGER ACCUMULATION OF 15-30MM/DAY AND MAXIMA OF
40-80MM ALSO ON FRIDAY-SATURDAY. THIS AFFECTS THE CAYMAN ISLES
EARLY ON SATURDAY MORNING...WITH ACCUMULATION OF 10-15MM/DAY AND
MAXIMA OF 20-35MM. OVER NORTHERN HONDURAS EXPECTING RAINFALL
AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 25-50MM ON
FRIDAY-SATURDAY...INCREASING TO 75-100MM/DAY AND MAXIMA OF
150MM-250MM AS OROGRAPHICALLY-FORCED MOISTURE CONVERGENCE PEAKS
ALONG THE NORTHERN COAST

SIMULTANEOUSLY...AS THE MID/UPPER LEVEL TROUGH AMPLIFIES ACROSS
THE USA...IT IS TO INDUCE THE NORTHWARD AMPLIFICATION OF A RIDGE
FROM THE EASTERN CARIBBEAN NORTHWARD TO THE WESTERN ATLANTIC EARLY
IN THE CYCLE. AS THE RIDGE BUILDS...A TROUGH TO THE EAST WILL
RELOCATE TO THE CENTRAL ATLANTIC EARLY ON FRIDAY MORNING. A
SUBTROPICAL JET MAXIMA BOUNDS THE SOUTHERN FRINGES OF THE UPPER
LEVEL TROUGH...WITH ENTRANCE AT 250 HPA JUST TO THE NORTH OF
PUERTO RICO/VIRGIN ISLES. THIS FAVORS AN UPPER DIVERGENT PATTERN
THAT IS TO PERSIST DURING THE NEXT TWO DAYS. LATER IN THE WEEK THE
JET MAXIMA IS TO ALSO PULL AWAY AS THE RIDGE BUILDS TO THE WEST.
BY MIDMORNING ON FRIDAY...AS THE RIDGE PATTERN STRENGTHENS OVER
THE WESTERN ATLANTIC...A STRONG SUBSIDENCE INVERSION IS TO
ESTABLISH ACROSS THE NORTHEAST CARIBBEAN ISLES. THIS IS TO THEN
FAVOR THE RAPID EROSION OF AVAILABLE MOISTURE FROM EAST TO WEST.
AT LOW LEVELS...THE TROUGH ALOFT SUSTAINS A SURFACE FRONT THAT
MEANDERS OVER THE VIRGIN ISLES-EASTERN PUERTO RICO TO THE BAHAMAS.
THE FRONT REMAINS NEARLY STATIONARY DURING THE NEXT COUPLE OF
DAYS...MEANWHILE WEAKENING AS IT LOSES ITS UPPER LEVEL SUPPORT.
BROAD POLAR RIDGE TO THE NORTH OF THE ISLANDS IS TO FAVOR BRISK
EASTERLY TRADES AND A COLD ADVECTIVE PATTERN ACROSS THE NORTHEAST
CARIBBEAN ISLES. THIS...IN-TURN...WILL RESULT IN SHALLOW
CONVECTION BUILDING TO THE EAST AND NORTH...STREAMING ACROSS THE
VIRGIN ISLES-PUERTO RICO-HISPANIOLA FROM TIME-TO-TIME. BRISK
EASTERLY TRADES ARE TO PERSIST ACROSS THE NORTHEAST CARIBBEAN
ISLES THROUGH THE END OF THE WEEK. THIS ALSO FAVORS A PREFRONTAL
SHEAR LINE OVER THE FRENCH ISLES TO THE EASTERN CARIBBEAN. THE
SHEAR LINE RAPIDLY MOVES ACROSS THE WINDWARD ISLES TO NORTHEAST
VENEZUELA-NORTHERN GUYANA LATER THIS EVENING. AS THE FRONT
MEANDERS ACROSS THE VIRGIN ISLES-PUERTO RICO IT IS TO RESULT IN
RAINFALL AMOUNTS OF 10-14MM/DAY AND MAXIMA OF 20-30MM THROUGH
EARLY THURSDAY. ON THURSDAY-FRIDAY THIS DECREASES TO 05-10MM/DAY
AND MAXIMA OF 15-25MM. OVER THE GUIANAS...THE SHEAR LINE WILL
TRIGGER RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM
THROUGH EARLY SATURDAY. MUCH LESSER AMOUNTS ARE EXPECTED TO THE
WEST OF THE SHEAR LINE IN THE WINDWARD ISLANDS AND NORTHEASTERN
VENEZUELA.

AT 250 HPA...A TUTT EXTENDS NORTH-TO-SOUTH BETWEEN 110W-85W ACROSS
THE EQUATOR TO 10S. THIS IS TO GENERALLY PERSIST OVER THE NEXT FEW
DAYS. EARLY IN THE CYCLE THIS IS TO ENHANCE CONVECTION ACROSS
EASTERN NICARAGUA TO FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND
MAXIMA OF 20-45MM THROUGH FRIDAY. OVER COSTA-RICA TO PANAMA THIS
IS TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM.
OVER WESTERN COLOMBIA...UNDER INFLUENCE OF THE PANAMANIAN
LOW/TROUGH...DEEP MOISTURE IS TO CONVERGE ALONG THE COAST. OVER
THE EJE CAFETERO TO THE NORTHWEST EXPECTING RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-20MM THROUGH EARLY
THURSDAY...INCREASING TO 10-15MM/DAY AND MAXIMA OF 20-35MM AFTER.
A SIMILAR TREND IS EXPECTED IN THE CAUCA VALLEY. ISOLATED HIGHER
AMOUNTS ARE EXPECTED IN THE CHOCO ON FRIDAY-SATURDAY. ON THE
ANDEAN REGION AND ACROSS EASTERN COLOMBIA/AMAZONIA EXPECTING
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM EARLY IN THE
CYCLE. IN THE AMAZON...ACCUMULATIONS ARE TO GRADUALLY INCREASE TO
10-15MM/DAY AND MAXIMA OF 20-35MM BY FRIDAY-SATURDAY.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL  24   36   48   60   72   84   96  TYPE  SOF
62W     65W  68W  70W  72W  74W  76W  78W  EW   14N
81W     83W  85W  87W  90W   DISSIPATES    EW   17N

AN EASTERLY WAVE ALONG 62W AND SOUTH OF 14N IS TO TRIGGER
SCATTERED CONVECTION ACROSS AMAZONIA IN SOUTHERN VENEZUELA TO
EASTERN COLOMBIA...WITH ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF
15-20MM. ON THE ANDEAN REGION OF COLOMBIA THIS IS TO ALSO SUSTAIN
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM ON
THURSDAY-FRIDAY...WITH HIGHER AMOUNTS ACROSS THE WESTERN COASTAL
PLAINS...WITH ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF 20-35MM.

AN EASTERLY WAVE ALONG 81W AND SOUTH OF 17N WILL SUSTAIN ORGANIZED
CONVECTION ACROSS EASTERN NICARAGUA...WITH ACCUMULATION OF
10-15MM/DAY AND MAXIMA OF 20-45MM ON WEDNESDAY AND THURSDAY. OVER
COSTA RICA EXPECTING LIGHT CONVECTION. WAVE IS TO DISSIPATE ON
FRIDAY.

PECK...MS (JAMAICA)
RIVAS...SENAMHI (PERU)
DAVISON/GALVEZ...WPC (USA)