Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 240159
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
959 PM AST Fri Feb 23 2018

.UPDATE...Passing showers increased over the local Atlantic waters
during the evening. These showers are expected to affect mainly
the eastern and northern portions of PR and the northern USVI.
Some of these showers could be heavy at times but overall they
should be brief. However, the frequency of showers are expected to
increase during the morning hours on Saturday, as more showers
across the Atlantic waters under a northeast flow will continue to
stream across the local area. No significant change from previous
forecast.


&&


.AVIATION Update...Mainly VFR conds expected to prevail early in
the fcst period. SHRA increasing from the Atlantic waters are
expected to affect at times after 08z TIST and the northern PR
terminals. Latest 24/00z indicated ENE winds between 8-34 kts
below FL100.


&&

.MARINE Update...Local buoys were indicating seas between 6-8
feet around 10-15 seconds during the past few hours and east to
northeast trades around 15 kt with gusts in the low 20s. Seas will
continue to slowly decrease through the weekend. However, rough
breaking wave action will continue to result in life threatening
rip currents along the northern exposed beaches of PR and portions
of the smaller islands through the weekend.


&&

.PREV DISCUSSION... /issued 404 PM AST Fri Feb 23 2018/

SYNOPSIS...Surface high pressure will hold across the western
Atlantic just north of the area while weakening over the weekend
and into early next week. As a result winds are expected to
diminish and hazardous marine conditions to subside. Moisture will
increase during the weekend and until early next week. A gradual
drying trend will then expected by mid week.

SHORT TERM...Tonight through Sunday...
Latest radar observations as well as satellite images depicted
small patches of cloudiness and showers across the Atlantic waters
moving from time to time across the local islands. This activity
will continue to affect mostly the U.S. Virgin Islands, Vieques,
Culebra as well the northern and eastern sections of Puerto Rico
tonight and Saturday morning with brief periods of moderate to
locally heavy rain. Due to the rapid movement of the showers, rainfall
amount are expected to be minimal but will produce hazardous
driving conditions. Some showers are also expected to develop
across the interior and western sections of Puerto Rico each
afternoon. A strong surface high pressure will hold across the
western Atlantic north of region while weakening until early next
week. This feature will remain as the main weather feature across
the local islands during the rest of the weekend and through
early next week.

An upper level trough is expected to remain from the Atlantic
waters southwestward across Hispaniola and Jamaica through the
weekend. The surface high pressure will continue to push patches
of moisture across the local islands, which will result in
showers activity across the region mostly during the overnight
and early morning hours. Then during the afternoon hours, this
moisture will combine with the upper level dynamic to result in
showers over the western portions of Puerto Rico as well as
downwind from the U.S. Virgin Islands each afternoon.

LONG TERM...Monday through Saturday...from previous
discussion... Surface high pressure will fade in the western
Atlantic just north of the local area early next week, but will be
replaced by a second high moving out of the eastern United States
Wednesday through Friday. The rumpled remains of a cold front
will pass through the area Monday through Tuesday next week with
continued shower activity, even while precipitable water values
trend downward from Sunday`s peak. This will be due to drying at
the top of the lower levels of the atmosphere. A drier and much
more stable air mass will be ushered in behind the remnants of the
cold front passage on Tuesday. This will limit shower activity
area- wide. Moist air behind a second front on Friday of next week
will prepare the area for possibly more shower activity and a
more vigorous pre-frontal trough early in the week after next.

AVIATION...VFR conds are expected to prevail through the forecast
cycle with VCSH at the Leeward and USVI terminals as well as
JSJ/JBQ. Isolated SHRA/-SHRA in and around JMZ through 23/22z. ENE
winds 15-20 knots with higher gusts, becoming at around 12 knots
overnight.

MARINE...Seas are expected to subside slowly tonight through
Sunday, such that by Sunday night all small craft advisories
should be down. Swell from a strong low in the northern Atlantic
mid week next week will send another surge of swell into the area
Wednesday night and Thursday when small craft advisories will
again be needed for the Atlantic waters and passages.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  73  82  73  83 /  60  60  60  60
STT  72  83  72  83 /  60  60  60  60

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late Saturday night for Culebra-
     Mayaguez and Vicinity-North Central-Northeast-Northwest-San
     Juan and Vicinity-Vieques-Western Interior.

     High Surf Advisory until 6 AM AST Saturday for Culebra-Mayaguez
     and Vicinity-North Central-Northeast-Northwest-San Juan and
     Vicinity-Southeast-Western Interior.

     High Rip Current Risk until 6 AM AST Saturday for Central
     Interior-Southeast.

VI...High Rip Current Risk through late Saturday night for St Croix.

     High Surf Advisory until 6 AM AST Saturday for St Croix-
     St.Thomas...St. John...and Adjacent Islands.

     High Rip Current Risk through Saturday afternoon for
     St.Thomas...St. John...and Adjacent Islands.

AM... Small Craft Advisory until 8 AM AST Sunday for Caribbean
      Waters of Puerto Rico from 10 NM to 17N-Coastal Waters of
 Northern Puerto Rico out 10 NM-Coastal Waters of Northern USVI
 and Culebra out 10 NM-Coastal Waters of Southern USVI Vieques
 and Eastern Puerto Rico out 10 NM-Mona Passage Southward to 17N.

     Small Craft Advisory until 2 PM AST Sunday for Anegada Passage
     Southward to 17N-Atlantic Waters of Puerto Rico and USVI
     from 10 NM to 19.5N.

     Small Craft Advisory until 2 AM AST Sunday for Coastal Waters OF
     Northwestern Puerto Rico out 10 NM.

&&

$$

SHORT TERM...DS
LONG TERM....JF


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