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Tropical Discussion
 
(Latest Discussion - Issued 1832Z Jul 27, 2017)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT THU JUL 27 2017

TROPICAL DISCUSSION FROM JUL 27/12 UTC: A 250 HPA HIGH OVER
NORTHERN TEXAS/ OKLAHOMA EXTENDS A RIDGE EAST ACROSS THE SOUTHERN
USA. AS THE UPPER RIDGE HOLDS TO THE NORTH...IT IS TO PROVIDE THE
STEERING FLOW TO A TUTT MOVING ACROSS NORTHERN MEXICO. LATER TODAY
THE TUTT IS TO MIGRATE ACROSS SONORA/NORTHERN SINALOA TO THE BAJA
PENINSULA. THE TUTT IS TO THEN WEAKEN LATER DURING THE WEEKEND. A
SECONDARY TUTT IS TO THEN RETROGRESS ACROSS THE NORTHERN
GULF...REACHING NORTHEAST MEXICO LATER ON FRIDAY/EARLY SATURDAY
MORNING. AS THE UPPER TROUGH MEANDERS ACROSS NORTHERN MEXICO EARLY
IN THE CYCLE...IT IS TO ENHANCE DIURNAL CONVECTION ALONG THE
SIERRA MADRE OCCIDENTAL. ACROSS SONORA-SINALOA-COLIMA AND NAYARIT
THIS IS TO INITIALLY FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND
MAXIMA OF 20-45MM. ON FRIDAY-SATURDAY THIS WILL SET AT 10-15MM/DAY
AND MAXIMA OF 20-30MM/DAY. ON THE CENTRAL-SOUTHWEST STATES OF
MEXICO...INITIALLY EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15MM. THROUGH SATURDAY EVENING THIS WILL INCREASE TO
10-15MM/DAY AND MAXIMA OF 20-30MM. OVER THE YUCATAN-SOUTHERN
MEXICO DIURNAL CONVECTION IS TO TRIGGER RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-20MM.

FARTHER EAST...AT 500 HPA...A HIGH TO THE NORTH-NORTHEAST OF THE
DOMINICAN REPUBLIC IS TO ANCHOR A SHORT WAVE RIDGE NORTH OF THE
ISLANDS. MID LEVEL RIDGE PATTERN IS TO REMAIN ILL ORGANIZED UNDER
PRESSURE FROM BROAD POLAR TROUGH TO THE NORTH OF 30N...AND DURING
THE WEEKEND IT IS TO NEARLY COLLAPSE OVER THE BAHAMAS/CUBA AS A
DEEPER TROUGH SETTLES ACROSS THE EASTERN USA/WESTERN ATLANTIC. AT
250 HPA... A TUTT/TUTT LOW OVERLAYS THE WANING MID LEVEL RIDGE
AXIS...WITH TROUGH EXTENDING OVER THE BAHAMAS-CUBA TO THE WESTERN
CARIBBEAN. THE TROUGH ALOFT IS TO PERSIST DURING THE NEXT 72-96
HRS. MEANWHILE...AS IT MEANDERS OVER CUBA...THE TROUGH WILL
ENHANCE DIURNAL CONVECTION...WITH RAINFALL AMOUNTS OF 05-10MM/DAY
AND MAXIMA OF 15-25MM/DAY. ON FRIDAY-SATURDAY THIS IS TO GRADUALLY
INCREASE TO 10-15MM/DAY AND MAXIMA OF 20-30MM/DAY. OVER THE
NORTHWEST BAHAMAS EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-20MM/DAY. THROUGH SATURDAY THIS INCREASES TO
10-15MM/DAY AND MAXIMA OF 20-30MM. THE TROUGH ALOFT TO ALSO
ENHANCE CONVECTION ACROSS JAMAICA...TO FAVOR RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-20MM. ON FRIDAY THIS INCREASES TO
10-15MM/DAY AND MAXIMA OF 20-30MM. 

ALTHOUGH WEAKENING...THE MID LEVEL CELL OF THE SUBTROPICAL RIDGE
NORTH OF THE GREATER ANTILLES REMAINS STRONG ENOUGH TO BLOCK A
TUTT/TUTT LOW TO THE NORTH-NORTHEAST OF THE ISLAND CHAIN. THE TUTT
LOW IS FORECAST TO SLOWLY WEAKEN WHILE DRIFTING TO THE
NORTH-NORTHEAST DURING THE NEXT FEW DAYS. AS THE TUTT WEAKENS AND
CONVECTIVE INSTABILITY WANES EXPECTING CONVECTION OVER THE EASTERN
CARIBBEAN ISLES TO ALSO WEAKEN EARLY IN THE CYCLE. INITIALLY
EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF
10MM...WITH FAIR WEATHER CONDITIONS TO THEN PREVAIL ON
FRIDAY-SATURDAY MORNING. THIS SETS THE STAGE FOR A SECONDARY TUTT
TO RETROGRESS ACROSS THE ISLAND CHAIN LATER ON FRIDAY/EARLY
SATURDAY MORNING. AS IT ENTERS THE NORTHEAST CARIBBEAN ISLES THIS
WILL ENHANCE CONVECTIVE INSTABILITY TO ONCE AGAIN FAVOR
ENVIRONMENTAL CONDITIONS FAVORABLE FOR SCATTERED CONVECTION TO
DEVELOP...TO SUSTAIN AN INCREASE IN CONVECTION ON SATURDAY-SUNDAY.
FURTHERMORE...PER THE CLIMATE FORECAST SYSTEM (CFS) AN ATMOSPHERIC
KELVIN WAVE IS TO PROPAGATE ACROSS THE CARIBBEAN DURING THE
WEEKEND. IN RESPONSE TO IMPROVING CONDITIONS THE GFS AND ECMWF
BOTH SHOW MODERATE TO HEAVY RAINFALL AMOUNTS TO AFFECT THE
NORTHEAST CARIBBEAN ISLES EARLY NEXT WEEK.

SOUTH OVER THE BASIN...AT 250 HPA...AN EAST-TO-WEST RIDGE EXTENDS
ALONG THE COAST OF VENEZUELA-NORTHERN COLOMBIA TO CENTRAL AMERICA.
AFOREMENTIONED TUTT...AS IT RETROGRESSES ACROSS THE ISLAND CHAIN
ON SATURDAY WILL THEN SUSTAIN EROSION OF SHORT WAVE RIDGE PATTERN
OVER THE EASTERN CARIBBEAN. IN RESPONSE...CONVECTION ACROSS
CENTRAL-EASTERN VENEZUELA TO NORTHERN GUYANA WILL INCREASE FROM
10-15MM/DAY AND MAXIMA OF 20-35MM EARLY IN THE CYCLE TO
10-15MM/DAY AND MAXIMA OF 20-45MM ON FRIDAY-SATURDAY. ACROSS
SURINAME-FRENCH GUIANA EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY
AND MAXIMA OF 15MM. OVER NORTHERN COLOMBIA-NORTHWEST VENEZUELA AND
ACROSS PANAMA...CONVECTION ALONG THE NEAR EQUATORIAL TROUGH/ITCZ
WILL RANGE BETWEEN 10-15MM/DAY AND MAXIMA OF 20-30MM/DAY...WITH
HIGHER AMOUNTS ON THE CHOCO/EJE CAFETERO OF WESTERN COLOMBIA WHERE
THE DAILY MAXIMA IS TO PEAK AT 25-50MM AS ENHANCED BY THE
PANAMANIAN LOW. OVER COSTA RICA-SOUTHERN NICARAGUA EXPECTING
RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 25-50MM. THROUGH
SATURDAY THE DAILY MAXIMA WILL DECREASE TO 20-40MM. OVER EL
SALVADOR-HONDURAS AND NORTHERN NICARAGUA EXPECTING RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. THROUGH FRIDAY
AFTERNOON THIS INCREASES TO 10-15MM/DAY AND MAXIMA OF 20-40MM.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL   24     36     48     60     72     84     96     TYPE
38W      41W    44W    48W    51W    55W    58W    62W  TUTT INDCD
61W      64W    67W    70W    73W    76W    79W    82W  TUTT INDCD
67W      70W    74W    77W    DISSIPATES                TUTT INDCD
77W      81W    84W    86W    88W   DISSIPATES          TUTT INDCD
94W      97W    99W   103W   106W   109W   111W   113W     TW

TUTT OVER THE TROPICAL ATLANTIC SUSTAINS AN INDUCED PERTURBATION
IN THE EASTERLY TRADES WITH AXIS ALONG 38W TO 28N. THIS MOVES TO
THE EASTERN CARIBBEAN ISLES EARLY ON SUNDAY MORNING...WHERE IT IS
TO TRIGGER RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM. ON
SUNDAY-MONDAY THE CONVECTION IS TO INTENSIFY WHILE BUILDING WEST
ACROSS THE VIRGIN ISLES TO PUERTO RICO.

THE TUTT NORTH OF THE LESSER ANTILLES SUSTAINS IN INDUCED TROUGH
IN THE EASTERLY TRADES WITH AXIS ALONG 61W TO 26N. OVER THE
LEEWARD-VIRGIN ISLES TO EASTERN PUERTO RICO THIS WILL SUSTAIN
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM. ACROSS PUERTO
RICO THIS IS TO THEN TRIGGER RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-20MM ON FRIDAY...WHILE ACROSS HISPANIOLA IT IS TO
SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM.
OVER EASTERN CUBA-SOUTHEAST BAHAMAS IT IS TO THEN TRIGGER RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM ON SATURDAY.

A TUTT INDUCED TROUGH EXTENDS ALONG 67W TO 23N. AS IT DECOUPLES
FROM THE TUTT ALOFT THE WAVE IS TO WEAKEN/DISSIPATE EARLY ON
SATURDAY MORNING. MEANWHILE...ACROSS HISPANIOLA THIS IS TO SUSTAIN
RAINFALL AMOUNTS OF 05-10MMD/AY AND MAXIMA OF 15-20MM. OVER
EASTERN CUBA-JAMAICA IT IS TO FAVOR RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-30MM ON FRIDAY.

ANOTHER WANING TUTT INDUCED TROUGH EXTENDS ALONG 77W TO 26N. THIS
WAVE TENDS TO WEAKEN AS IT MOVES ACROSS THE YUCATAN PENINSULA
EARLY ON SATURDAY. MEANWHILE...OVER WESTERN CUBA AND THE NORTHWEST
BAHAMAS THIS IS TO SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-20MM. ON FRIDAY TO SATURDAY THIS INCREASES TO
10-15MM/DAY AND MAXIMA OF 20-30MM. OVER THE YUCATAN THIS IS TO
THEN TRIGGER RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM
ON SATURDAY.

A TROPICAL WAVE ALONG 94W AND SOUTH OF 19N IS TO SUSTAIN SCATTERED
CONVECTION ACROSS SOUTHWEST-CENTRAL MEXICO WITH ACCUMULATION OF
05-10MM/DAY AND MAXIMA OF 15-20MM THROUGH FRIDAY EVENING.
THEREAFTER...ASSOCIATED CONVECTION IS TO LIMIT TO THE EASTERN
PACIFIC ITCZ.

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