368  
FXCA20 KWBC 161921  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
220 PM EST THU NOV 16 2017  
 
TROPICAL DISCUSSION FROM NOV 16/12 UTC: WEST OVER THE DOMAIN...AT  
500/250 HPA...BROAD RIDGE DOMINATES THE FLOW ACROSS MEXICO AND THE  
SOUTHWEST USA WHILE CENTERING ON A CLOSED HIGH OVER THE SOUTHERN  
BAJA PENINSULA. BROAD UPPER RIDGE PATTERN IS TO PERSIST THROUGH  
SATURDAY MORNING...WHILE THE ASSOCIATED MID LEVEL HIGH RELOCATES  
TO NORTHEAST MEXICO. LATER IN THE DAY...IT WILL START TO CRUMBLE  
UNDER PRESSURE FROM AMPLIFYING POLAR TROUGH OVER THE USA.  
MEANWHILE...THE MID LEVEL RIDGE IS TO SUSTAIN A STRONG CAP  
INVERSION ACROSS CENTRAL/NORTHERN STATES OF MEXICO...WHERE IT IS  
TO CONTINUE INHIBITING ORGANIZED DEEP CONVECTION DURING THE NEXT  
FEW DAYS.  
 
DOWNSTREAM FROM THE CONTINENTAL RIDGE...A 500/250 HPA TROUGH  
EXTENDS OVER THE WESTERN ATLANTIC TO THE WESTERN CARIBBEAN. THE  
RIDGE TO THE WEST IS STEERING SHORT WAVE PERTURBATIONS AROUND THIS  
TROUGH...LEADING TO GRADUAL AMPLIFICATION OF THE LONG WAVE AXIS  
ACROSS THE WESTERN CARIBBEAN TO CENTRAL AMERICA/CENTRAL CARIBBEAN  
EARLY ON FRIDAY. DURING THE WEEKEND THE TROUGH ALOFT IS TO THEN  
START A SLOW DECAYING PROCESS...WITH BROAD UPPER TROUGH WEAKENING  
TO A NARROW SHEAR AXIS OVER THE CENTRAL CARIBBEAN BEFORE LIFTING  
OVER BUILDING CELL OF THE SUBEQUATORIAL RIDGE TO THE EAST. THE  
SUBEQUATORIAL RIDGE EXTENDS FROM SOUTHWEST TO NORTHEAST FROM  
NORTHERN SOUTH AMERICA...ACROSS THE ISLAND CHAIN TO THE EASTERN  
ATLANTIC. OVER THE ISLAND CHAIN-CENTRAL TROPICAL ATLANTIC THE  
RIDGE FAVORS A MID LEVEL CONVERGENT PATTERN THAT IS INHIBITING  
ORGANIZED DEEP CONVECTION.  
 
AT LOW LEVELS...MEANDERING FRONT OVER THE BAHAMAS-CUBA IS FORECAST  
TO FRONTOLIZE EARLY IN THE CYCLE. A SECONDARY FRONT  
FOLLOWS...SURGING TO THE NORTHWEST BAHAMAS LATER TODAY...MEANWHILE  
FAVORING A PREFRONTAL SHEAR LINE OVER THE CENTRAL BAHAMAS TO CUBA.  
ON FRIDAY THE SHEAR LINE MOVES TO THE TURKS-EASTERN CUBA...WHERE  
IT IS FORECAST TO WEAKEN. MOST ACTIVE CONVECTION IS EXPECTED IN  
ASSOCIATION WITH THE SHEAR LINE. OVER THE NORTHWEST BAHAMAS THE  
SHEAR LINE WILL SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA  
OF 15-25MM...WHILE ACROSS CENTRAL/WESTERN CUBA THIS IS TO FAVOR  
RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM. AS IT MOVES TO  
EASTERN CUBA-SOUTHEAST BAHAMAS/THE TURKS ON FRIDAY IT IS TO  
SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM.  
ALSO AT LOW LEVELS...A POLAR RIDGE OVER THE GULF SUSTAINS A LIGHT  
NORTHERLY FLOW ACROSS THE GULF-CUBA TO THE WESTERN  
CARIBBEAN/NORTHERN CENTRAL AMERICA. OVER SOUTHERN MEXICO THIS IS  
TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM  
THROUGH FRIDAY MORNING...WHILE ACROSS NORTHERN HONDURAS-CENTRAL  
GUATEMALA/SOUTHERN BELIZE EXPECTING RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15MM THROUGH FRIDAY EVENING.  
 
THE TROUGH OVER THE WESTERN ATLANTIC-WESTERN CARIBBEAN IS  
INTERACTING WITH A LOW LEVEL TROUGH OVER THE CENTRAL CARIBBEAN.  
THE TROUGH EXTENDS TO THE SOUTHWEST FROM HAITI TO PANAMA/SOUTHERN  
CARIBBEAN. ON FRIDAY IT SLIDES EAST TO EXTEND OVER THE DOMINICAN  
REPUBLIC TO THE GULF OF URABA/NORTHERN COLOMBIA. MEANWHILE...THE  
TROUGH IS TO FAVOR A MOIST SOUTHWESTERLY FLOW ACROSS THE CENTRAL  
CARIBBEAN...WITH MOISTURE TO CONVERGE ACROSS SOUTHERN  
HISPANIOLA-PUERTO RICO. PWAT CONTENT DURING THE NEXT COUPLE OF  
DAYS WILL RANGE BETWEEN 50-75MM. BUT AS THE UPPER LEVEL TROUGH  
WEAKENS ON SATURDAY-SUNDAY THIS WILL DECREASES TO 50MM. UNDER  
FAVORABLE JET DYNAMICS...AND AS SHORT WAVE VORTICES LIFT ACROSS  
THE CENTRAL CARIBBEAN...THE ENVIRONMENTAL CONDITIONS WILL REMAIN  
HIGHLY CONDUCIVE TO GENERATION OF MESO SCALE CONVECTIVE SYSTEMS.  
ACROSS SOUTHERN HISPANIOLA EXPECTING RAINFALL AMOUNTS OF  
35-70MM/DAY AND MAXIMA OF 125-200MM. ON FRIDAY...THE FOCUS OF THE  
HEAVY CONVECTION GRADUALLY SHIFTS TO THE DOMINICAN REPUBLIC SIDE  
OF THE ISLAND...WHERE IT WILL SUSTAIN RAINFALL AMOUNTS OF  
20-40MM/DAY AND MAXIMA OF 50-100MM. ON SATURDAY IT DECREASES TO  
15-20MM/DAY AND MAXIMA OF 30-60MM. ACROSS PUERTO RICO THIS IS TO  
FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. ON  
FRIDAY THE MAXIMA INCREASES TO 20-45MM/DAY...WHILE ON SATURDAY  
EXPECTING ACCUMULATION OF 15-20MM/DAY AND MAXIMA OF 30-60MM. OVER  
JAMAICA...MEANWHILE...EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY  
AND MAXIMA OF 10MM OVER THE NEXT COUPLE OF DAYS.  
 
OVER THE SOUTHERN CARIBBEAN...IN INTERACTION WITH THE EASTERN  
PACIFIC ITCZ...THIS IS TO FAVOR HEAVY CONVECTION ACROSS WESTERN  
PANAMA AND PORTIONS OF COSTA RICA... WITH ACCUMULATION OF  
35-70MM/DAY AND MAXIMA OF 75-100MM. ON FRIDAY-SATURDAY THIS  
DECREASES TO 05-10MM/DAY AND MAXIMA OF 15MM. ACROSS NORTHERN COSTA  
RICA/SOUTHERN NICARAGUA DIURNAL CONVECTION IS TO RESULT IN  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM THROUGH  
FRIDAY MORNING. OVER WESTERN COLOMBIA/ANDEAN REGION...AS THE ITCZ  
MEANDERS NORTH OF ITS CLIMATOLOGICAL POSITION...DIURNAL CONVECTION  
IS TO FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM.  
ON FRIDAY...AS THE LOW LEVEL TROUGH MOVES TO THE GULF OF  
URABA...EXPECTING HIGHER RAINFALL AMOUNTS OVER NORTHERN COLOMBIA  
TO EASTERN PANAMA WITH ACCUMULATION OF 15-20MM/DAY AND MAXIMA OF  
30-60MM. ON SATURDAY THIS IS TO THEN FAVOR RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-45MM WHILE BUILDING EAST INTO  
NORTHWEST VENEZUELA. ACROSS VENEZUELA EXPECTING RAINFALL AMOUNTS  
OF 05-10MM/DAY AND MAXIMA OF 15-25MM...WITH MOST ACTIVE INITIALLY  
TO CLUSTER OVER AMAZONIA TO THE SOUTH.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
41W 42W 44W 46W 48W 50W 52W 54W EW 12N  
65W 66W 68W 69W 70W 71W 72W 73W EW 16N  
 
AN EASTERLY WAVE IS INITIALIZED ALONG 41W TO 12N. THIS REACHES  
FRENCH GUIANA LATER ON SATURDAY TO FAVOR RAINFALL AMOUNTS OF  
00-05MM/DAY AND MAXIMA OF 10MM.  
 
AN EASTERLY WAVE ALONG 65W AND SOUTH OF 16N IS TO SUSTAIN  
SCATTERED CONVECTION ACROSS VENEZUELA TO EASTERN COLOMBIA WITH  
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-25MM. ACROSS  
NORTHWEST VENEZUELA TO NORTHERN COLOMBIA THIS IS TO THEN FAVOR  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-45MM.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  
 

 
 
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