Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2
000
FXCA20 KWBC 181931
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
231 PM EST MON DEC 18 2017

TROPICAL DISCUSSION FROM DEC 18/12 UTC: FAIR WEATHER CONDITIONS
AND VERY LIGHT RAINFALL ACCUMULATIONS ARE EXPECTED ACROSS THE
BASIN THROUGH THE FORECAST CYCLE. THIS IS BECAUSE OF THE INFLUENCE
OF A LARGE AND ROBUST MID-LEVEL RIDGE THAT IS FORECAST TO EXTEND
ACROSS MOST OF THE NORTHERN-CENTRAL CARIBBEAN THROUGH THE CYCLE.

AT UPPER LEVELS...A LARGE AND PERSISTENT RIDGE IS FORECAST TO
CONTINUE EXTENDING OVER MOST OF THE CARIBBEAN WHILE CENTERING ON A
HIGH OVER NORTHERN COLOMBIA/SOUTHERN CARIBBEAN. UPPER TROUGHS WILL
MEANDER ALONG THE PERIPHERY OF THIS RIDGE. IN MEXICO...THESE WILL
PROPAGATE FROM SOUTHWEST TO NORTHEAST ALONG NORTHWESTERN
MEXICO/SOUTHWESTERN UNITED STATES. IN THE ATLANTIC OCEAN...THESE
WILL PROPAGATE FROM NORTHWEST TO SOUTHEAST TOWARDS THE CENTRAL
TROPICAL ATLANTIC. AT MID-LEVELS MODELS ALL AGREE ON A STRONG
MID-LEVEL RIDGE STRENGTHENING ACROSS THE NORTHERN CARIBBEAN. THE
CENTER OF THE RIDGE WILL MEANDER BETWEEN THE EASTERN GULF OF
MEXICO/FLORIDA/THE BAHAMAS...YET IT WILL EXTEND INTO EQUATORIAL
LATITUDES OF SOUTH AMERICA. THE RIDGE WILL CONTINUE STRENGTHENING
THE CURRENT SUBSIDENCE CAP...AND WILL CONTINUE LIMITING ANY
VERTICAL DEVELOPMENT TO SHALLOW CUMULUS CAPABLE OF PRODUCING ONLY
LIGHT RAIN SHOWERS. AREAS WITH MODERATE PRECIPITATION IN THE
FORECAST DOMAIN WILL LIMIT TO THE GUIANAS AND THE CENTRAL AMAZON
BASIN.

IN MEXICO...A SUBTROPICAL MOISTURE PLUME IS WANING WHILE STILL
ENHANCING LIGHT RAIN SHOWERS ACROSS SINALOA/NAYARIT INTO
NORTHEASTERN MEXICO. THIS IN INTERACTION WITH STRONG UPPER TROUGH
MEANDERING ACROSS NORTHWESTERN MEXICO TOWARDS NEW MEXICO/TEXAS.
THROUGH EARLY TUESDAY...EXPECTING 05-10MM/DAY AND MAXIMA OF 15MM
ACROSS SINALOA/NAYARIT...WHILE MAXIMA UNDER 10MM IS EXPECTED
ELSEWHERE ACROSS ZACATECAS/DURANGO/COAHUILA. A SIGNIFICANT DRYING
TREND FOLLOWS.

ACROSS THE NORTHERN AND EASTERN CARIBBEAN...UNDER THE INFLUENCE OF
THE STRONG MID-LEVEL RIDGE...ACTIVITY WILL BE CONSTRAINED TO LIGHT
RAIN SHOWERS. TRADE WINDS ARE FORECAST TO REMAIN FROM THE
EAST-NORTHEAST AND ACCELERATED THROUGH THE CYCLE. WIND SPEEDS WILL
RANGE BETWEEN 15-25KT RANGE TO THE SOUTH OF 22N...AND 10-20KT FROM
22N TO 25N. THIS WILL CONTINUE FAVORING SHALLOW INSTABILITY AND
FAST-MOVING LIGHT TRADE WIND SHOWERS ACROSS THE EASTERN AND
NORTHEASTERN COASTS OF CUBA...HISPANIOLA...PUERTO RICO AND MOST OF
THE LESSER ANTILLES. RAINFALL ACCUMULATIONS WITH THESE PERSISTENT
SHOWERS WILL BE UNDER 10MM/DAY. EXCEPTIONS WILL BE ISOLATED HIGHER
AMOUNTS ALONG NORTHEASTERN COASTS OF HISPANIOLA...WHERE ENHANCED
OROGRAPHIC UPLIFT WILL LEAD TO LOCALIZED MAXIMA.

UNDER THE STRENGTHENING OF THE TRADES...THE CARIBBEAN LOW-LEVEL
JET IS INTENSIFYING. MODELS ARE SUGGESTING WIND SPEEDS EXCEEDING
35-45KT TO THE NORTH OF NORTHERN COLOMBIA/NORTH OF THE
ABC...STRETCHING WEST INTO THE NICARAGUA COAST. THIS IS TO LAST
THROUGH WEDNESDAY...WHEN TRADES ARE FORECAST TO WEAKEN
SLIGHTLY...LEADING TO A WEAKENING OF THE LOW-LEVEL JET TO 25-35KT.
THE STRONG LOW-LEVEL JET IS FAVORING MOISTURE CONVERGENCE ALONG
THE CARIBBEAN COAST OF CENTRAL AMERICA...ESPECIALLY FROM WESTERN
PANAMA ACROSS COSTA RICA INTO NICARAGUA/EASTERN HONDURAS. ALTHOUGH
A MOIST PLUME IS IN PLACE...THE RAPID MOVEMENT OF THE SHOWERS WILL
LIMIT POTENTIAL RAINFALL ACCUMULATIONS. THROUGH EARLY
WEDNESDAY...STREAMING SHOWERS WILL LEAD TO 05-10MM/DAY AND MAXIMA
OF 15MM ACROSS COSTA RICA AND EASTERN NICARAGUA. BY WEDNESDAY INTO
THURSDAY...FOCUS OF CONVERGENCE WILL CONCENTRATE IN SOUTHERN
NICARAGUA/WESTERN PANAMA...WHERE EXPECTING 10-15MM/DAY AND MAXIMA
OF 20-30MM.

IN NORTHERN SOUTH AMERICA...LARGEST ACCUMULATIONS ARE EXPECTED IN
THE GUIANAS IN ASSOCIATION WITH ITCZ CONVERGENCE. DEEP-MOIST LAYER
IS CONSTRAINING TO LATITUDES TO THE SOUTH OF 02N/03N...WHILE A DRY
AIR MASS CONTINUES IN PLACE IN THE CENTRAL AND NORTHERN GUIANAS
OVER 500 HPA. THIS WILL CONTINUE LIMITING ACCUMULATIONS TO SUSTAIN
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM ON
MONDAY-TUESDAY...DECREASING GRADUALLY ON 05-10MM/DAY AND MAXIMA OF
15-20MM ACROSS THE SOUTHERN GUIANAS ON WEDNESDAY-THURSDAY. ALSO IN
NORTHERN SOUTH AMERICA...ENHANCED MOISTURE CONVERGENCE WHERE A
TRADE WIND MOIST PLUME INTERACTS WITH THE COAST...WILL LEAD TO
SCATTERED SHOWERS IN TRINIDAD AND TOBAGO/NORTHEASTERN VENEZUELA
THROUGH THE CYCLE. THIS WILL LEAD TO ACCUMULATIONS OF 05-10MM/DAY
AND ISOLATED MAXIMA OF 15MM. IN COLOMBIA...ACTIVITY WILL BE
CONSTRAINED TO THE PACIFIC BASIN...WHERE ITCZ CONVERGENCE WILL
FAVOR 05-10MM/DAY AND MAXIMA OF 15MM THROUGH EARLY WEDNESDAY. THIS
IS INCREASING TO 10-15MM/DAY AND MAXIMA OF 20-30MM IN SOUTHWESTERN
COLOMBIA BY WEDNESDAY-THURSDAY.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL  24   36   48   60   72    84     96       TYPE     SOF
80W     82W   85W  87W  90W  93W  96W    100W      EW       17N

AN ILL-DEFINED EASTERLY WAVE IS INITIALIZED AT 80W AND TO THE
SOUTH OF 17N. THIS WAVE WILL RAPIDLY CROSS CENTRAL AMERICA ON
MONDAY/TUESDAY...PRODUCING LIMITED EFFECTS ON PRECIPITATION.

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

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.