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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1733Z Apr 06, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
133 PM EDT MON APR 06 2020

TROPICAL DISCUSSION FROM APRIL 6/18 UTC: THE ANALYSIS OF
TROPOSPHERIC EQUATORIAL WAVES SHOWS THE DIVERGENT PHASE OF THE
MADDEN-JULIAN OSCILLATION PROPAGATING ACROSS THE DATE LINE/CENTRAL
PACIFIC. THE CFS SHOW THE DIVERGENT PHASE ENTERING MEXICO ON
WEDNESDAY APRIL 8...AND PEAKING ACROSS CENTRAL AMERICA...WESTERN
SOUTH AMERICA AND THE WESTERN CARIBBEAN BETWEEN APRIL 10 AND 16.
THIS SHOULD STIMULATE THE COVERAGE AND INTENSITY OF
PRECIPITATION...DEPENDING ON WHICH WEATHER SYSTEMS ARE IN PLACE AT
THE TIME. IN THE MEAN TIME...LARGE SCALE TROPOSPHERIC CONDITIONS
OVER THE BASIN ARE SLIGHTLY CONVERGENT. THEY BECOME MORE NEUTRAL
THROUGH THE FORECAST CYCLE/INTO LATE IN THE WORK WEEK.

NORTH IN THE DOMAIN...A SURFACE FRONT EXTENDS INTO SOUTHERN
CALIFORNIA. THE FRONT WILL ENTER EXTREME NORTWEST BAJA CALIFORNIA
ON EARLY HOURS OF TUESDAY. BY TUESDAY EVENING IT WILL EXTEND FROM
JUST WEST OF MEXICALI INTO EL ROSARIO IN NORTHWEST CALIFORNIA. BY
WEDNESDAY EVENING THE FRONT WILL EXTEND FROM JUST WEST OF
PHOENIX...NORTHWEST SONORA INTO BAHIA TORTUGAS IN NORTHERN BAJA
CALIFORNIA SUR...WHERE IT WILL BE LOSING DEFINITION. THIS WILL
SUSTAIN ACCUMULATIONS OF 05-10MM/DAY AND MAXIMA OF 15MM ON A DAILY
BASIS...AS STIMULATED BY THE UPPER TROUGH AND BY THE INCREASINGLY
DIVERGENT PATTERN IN THE UPPER TROPOSPHERE. NOTE THAT THE AIR MASS
WILL BE COME SUFFICIENTLY COLD ON WEDNESDAY EVENING TO SUSTAIN
SNOWFALL IN THE SIERRA PEDRO MARTIR IN NORTHERN BAJA CALIFORNIA.
ALSO IN NORTHERN MEXICO...AS MOIST SOUTHWESTERLY FLOW CONTINUES IN
THE UPPER LEVELS...EXPECTING NUMEROUS SHORT WAVE PERTURBATIONS TO
INDUCE ASCENT THROUGH THE CYCLE. THESE WILL SUSTAIN DAILY ISOLATED
STRONG THUNDERSTORMS IN NORTHEAST MEXICO TO SUSTAIN 05-10MM/DAY
AND MAXIMA OF 15MM IN COAHUILA ON MONDAY AND TUESDAY...INCREASING
TO 05-10MM/DAY AND MAXIMA OF 25MM ON WEDNESDAY WHEN A SLIGHT
CHANCE FOR SEVERE CONVECTION IS EXPECTED. ALSO IN NORTHERN
MEXICO...THE DIVERGENT ENTRANCE OF AN UPPER JET AND THE APPROACH
OF AN UPPER TROUGH ON MONDAY WILL DEVELOP PRECIPITATION IN THE
SIERRA MADRE OCCIDENTAL OF SOUTHERN SONORA/NORTHERN SINALOA TO
SUSTAIN 05-10MM/DAY AND MAXIMA OF 15MM. DOWNSTREAM ACROSS CENTRAL
CHIHUAHUA EXPECTING 00-05MM/DAY AND MAXIMA OF 10MM.

TO THE SOUTHEAST OF THESE REGION AND AT MID-LEVELS...MID-LEVEL
RIDGE DOMINATES A WIDE BELT FROM CENTRAL/SOUTHERN MEXICO INTO THE
ARC OF THE LESSER ANTILLES. THIS IS LIMITING CONVECTION. THE ONLY
SIGNIFICANT CONVECTION IN THE BASIN IS OCCURRING ALONG A SURFACE
FRONT IN THE NORTHWEST BAHAMAS AND IN PUERTO RICO. THE MID-LEVEL
RIDGE PATTERN WILL BE THE DOMINANT FEATURE THROUGH THE FORECAST
CYCLE...TO CONTINUE SUSTAINING GENERALLY FAIR WEATHER CONDITIONS
IN THE CARIBBEAN BASIN AND SOUTHERN MEXICO THROUGH THE FORECAST
CYCLE. WEST IN THE DOMAIN...UNDER THE INFLUENCE OF THE RIDGE
PATTERN...EXPECTING LIMITED ACCUMULATIONS. IN MEXICO...THIS WILL
SUSTAIN 00-05MM/DAY AND MAXIMA OF 10MM ON A DAILY BASIN ALONG THE
SOUTHERN SIERRA MADRE ORIENTAL AND EASTERN PORTIONS OF THE EJE
VOLCANICO. IN GUATEMALA/CHIAPAS EXPECTING 05-10MM/DAY AND ISOLATED
MAXIMA OF 15MM ON MONDAY DECREASONG TO 00-05MM/DAY AND MAXIMA OF
10M THEAFTER...TO DEVELOP ON A DAILY BASIS.

HOWEVER...AS THE RIDGE STRENGTHENS OVER THE YUCATAN PENINSULA INTO
THE GULF OF HONDURAS...THROUGH THE FORECAST CYCLE...IT WILL
INCREASE THE ADVECTION OF COOLER AIR IN THE SOUTHEAST USA INTO THE
TROUGH PATTERN PERSISTING TO THE NORTH OF HISPANIOLA...PUERTO RICO
AND THE VIRGIN AND LEEWARD ISLANDS. THIS WILL ALLOW THE
PROPAGATION OF SHORT WAVE TROUGHS...THAT IN INTERACTION WITH THE
SURFACE FRONT AND SHEAR LINE WILL SUSTAIN ROUNDS OF MODERATE
PRECIPITATION ESPECIALLY IN PUERTO RICO. WITH REGARDS TO THE
SURFACE FRONT...ON MONDAY EVENING...IT IS FORECAST TO EXTEND
ACROSS PUERTO RICO...THE NORTHERN TIER OF THE DOMININCAN REPUBLIC
AND ALONG THE WESTERN BAHAMAS INTO SOUTH FLORIDA. BY TUESDAY
EVENING IT WILL EXTEND ACROSS THE NORTHERN LEEWARD ISLANDS AND
NORTHERN PUERTO RICO...NORTHERN DOMINICAN REPUBLIC...INTO THE
NORTHWEST BAHAMAS. BY WEDNESDAY EVENING IT WILL EXTEND ALONF 20N
FROM 55W INTO 68W AND THEN TO THE TURKS AND CAICOS. THE SHEAR LINE
IS FORECAST TO EXTEND ACROSS THE LEEWARD AND SOUTHERN VIRGIN
ISLANDS ON MONDAY...CENTRAL LEEWARD ISLANDS ON TUESDAY...AND
NORTHERN LEEWARD ISLANDS...PUERTO RICO AND SOUTHERN HISPANIOLA ON
WEDNESDAY. THIS WILL SUSTAIN PRECIPITATION. ON MONDAY...LARGEST
ACCUMULATIONS ARE EXPECTED IN PUERTO RICO WHERE FRONTAL
CONVERGENCE WILL INTERACT WITH THE DIURNAL CYCLE OF HEATING TO
SUSTAIN 10-15MM/DAY AND ISOLATED MAXIMA OF 20-45MM IN PUERTO RICO.
IN THE NORTHWEST BAHAMAS...SURFACE LOW ALONG THE REMNANTS OF THE
FRONT WILL SUSTAIN ADDITIONAL ASCENT TO PRODUCE 05-10MM/DAY AND
MAXIMA OF 15-25MM. IN THE LEEWARD ISLANDS...FRONTAL AND SHEAR LINE
CONVERGENCE WILL SUSTAIN 00-05MM/DAY AND MAXIMA OF 10MM. IN
HISPANIOLA...DIURNAL HEATING WILL SUSTAIN 05-10MM/DAY AND MAXIMA
OF 15MM. BY TUESDAY...LARGEST ACCUMULATIONS ARE EXPECTED IN PUERTO
RICO WHERE FRONTAL CONVERGENCE WILL SUSTAIN 10-15MM/DAY AND MAXIMA
OF 20-35MM. IN HISPANIOLA EXPECTING MAXIMA OF 15MM AND MAXIMA OF
10MM IN THE NORTHWEST BAHAMAS. IN THE LEEWARD AND VIRGIN
ISLANDS...FRONTAL AND SHEAR LINE CONVERGENCE WILL SUSTAIN MAXIMA
OF 15MM. BY WEDNESDAY...THE MOISTURE CONVERGENCE ASSOCIATED WITH
THE WEAKER SHEAR LINE WILL INTERACT WITH A SHORT WAVE TROUGH IN
THE MID-LEVELS TO SUSTAIN A PEAK IN PRECIPITATION IN PUERTO RICO.
EXPECTING 15-20MM/DAY AND ISOLATED MAXIMA OF 30-60MM. IN THE
LEEWARD ISLANDS AND VIRGIN ISLANDS EXPECTING 05-10MM/DAY AND
MAXIMA OF 15MM. IN SOUTHERN HISPANIOLA EXPECTING 05-10MM/DAY AND
MAXIMA OF 15MM.

IN THE UPPER TROPOSPHERE OF SOUTHERN CENTRAL AMERICA/NORTHERN
CENTRAL AMERICA/SOUTHERN CARIBBEAN...THE SUBEQUATORIAL RIDGE HAS
NOW BUILT INTO THE CARIBBEAN COAST. THIS HAS DECREASED THE SHEAR
AND THE ADVECTION OF DRY AIR FROM THE TROPICAL PACIFIC...WHICH IS
ALLOWING THE GRADUAL ACTIVATION OF CONVECTION IN THE EXTREME
SOUTHERN CARIBBEAN AND PANAMA. IN THE MID-LEVELS...WEAK EASTERLY
FLOW PREVAILS IN SOUTHERN CENTRAL AMERICA ON MONDAY...WHICH ARE
FORECAST TO INTENSIFY AS THE RIDGE STRENGTHENS TO THE NORTH.
ALTHOUGH EASTERLY FLOW IS NOT NECESSARILY DETRIMENTAL FOR
CONVECTION...THE AIR MASS IS EXTREMELY DRY. THIS WILL SUSTAIN
CONSERVATIVE RAINFALL ACCUMULATIONS IN REGIONS OVER AND WEST OF
THE PANAMA ISTHMUS. ON MONDAY...EXPECTING 05-10MM/DAY AND MAXIMA
OF 15MM BETWEEN SOUTHEAST NICARAGUA AND EASTERN/SOUTHERN COSTA
RICA AND NORTHWEST PANAMA. BY TUESDAY...AN INCREASE IN LOW-LEVEL
MOISTURE CONVERGENCE WILL SUSTAIN AN INCREASE IN ACCUMULATIONS FO
05-10MM/DAY AND MAXIMA OF 15-20MM IN BOCAS DEL TORO IN PANAMA AND
IN EASTERN COSTA RICA. NORTH INTO EASTERN HONDURAS EXPECTING
00-05MM/DAY AND ISOLATED MAXIMA OF 10MM. BY WEDNESDAY...EXPECTING
05-10MM/DAY AND MAXIMA OF 15MM IN WESTERN PANAMA AND IN EASTERN
AND SOUTHERN COSTA RICA.

TO THE EAST...MODELS FORECAST A GRADUAL INTENSIFICATION OF THE
PANAMA TROUGH/LOW PATTERN. THIS WILL ENHANCE MOISTURE CONVERGENCE
ALONG NORTHWEST COLOMBIA TO SUSTAIN A GRADUAL INCREASE IN
ACCUMULATIONS THROUGH THE CYCLE. INITIALLY...EXPECTING 10-15MM/DAY
AND MAXIMA OF 20-35 ALONG THE WEST COAST FROM THE CENTRAL CHOCO
INTO NORTHERN ECUADOR. ACROSS NORTHWEST COLOMBIA INTO THE BAJO
MAGDALENA AND CENTRAL ANDES...EXPECTING 05-10MM/DAY AND MAXIMA OF
15-20MM. BY TUESDAY...LARGEST ACCUMULATIONS CONCENTRATE IN
NORTHWEST COLOMBIA/EASTERN PANAMA WHERE EXPECTING 10-15MM/DAY AND
MAXIMA OF 20-35MM. ELSEWHERE IN THE ANDES OF CENTRAL /NORTHERN
COLOMBIA AND INTO THE LAKE MARACAIBO REGION EXPECTING 05-10MM/DAY
AND MAXIMA OF 15-20MM. BY WEDNESDAY...AS PANAMANIAN LOW
INTENSIFIES EXPECTING AN INCREASE IN ACCUMULATIONS IN NORTHWEST
COLOMBIA AND EASTERN PANAMA TO SUSTAIN 15-20MM/DAY AND MAXIMA OF
25-50MM. ELSEWHERE IN ANDEAN COLOMBIA EXPECTING 05-10MM/DAY AND
MAXIMA OF 15-20MM.

EAST OF THE ANDES...LARGEST AMOUNTS WILL CLUSTER ALONG THE NET IN
THE AMAZON BASIN...WHERE EXPECTING 15-20MM/DAY AND MAXIMA OF
30-70MM IN A DAILY BASIS...TO COVER SOUTHEAST COLOMBIA/NORTHWEST
BRAZIL AND EXTREME SOUTHERN VENEZUELA. IN THE ORINOQUIA OF
NORTHERN COLOMBIA EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM
THROUGH EARLY WEDNESDAY...THEN DECREASING TO 05-10MM/DAY AND
MAXIMA OF 15-20MM. EAST IN THE GUIANAS...ACTIVITY WILL FLARE UP IN
THE SOUTHERN THIRD OF THE COUNTRIES ON A DAILY BASIS. A
PERTURBATION CROSSES SURINAME ON TUESDAY...TO SUSTAIN DEEP
CONVECTION IN MOST OF THE COUNTRY WITH ACCUMULATIONS OF
15-20MM/DAY AND ISOLATED MAXIMA OF 35-70MM. THIS DECREASES ON
WEDNESDAY TO 05-10MM/DAY AND MAXIMA OF 15-20MM WHILE STRONGER
CONVECTION REMAINS TO THE SOUTH OF THE BRAZIL BORDER.

GALVEZ/DAVISON...WPC (USA)