Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 160030
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
830 PM AST Fri Dec 15 2017

.UPDATE...Doppler radar detected only isolated showers mostly
across the surrounding waters, with few of them affecting the
eastern sections of Puerto Rico as well as the northern U.S.
Virgin Islands from time to time. However, not significant
precipitation was detected elsewhere across the local islands.
Local weather conditions will continue to be dominated by a strong
upper level ridge over the area. Under this ridge pattern aloft,
continue to expect fair weather conditions with trade wind showers
at times as well as locally induced showers across the southwest
quadrant of Puerto Rico each afternoon and pleasant daytime and
overnight temperatures during the next few days. A developing
surface high pressure across the northeast central Atlantic will
continue to maintain an east to east-northeast wind flow across
the region for the next couple of days.

&&

.AVIATION...A north swell between 4-6 feet will continue to affect
the Atlantic waters and passages overnight. This will result in a
high risk of rip currents across the Atlantic beaches of Puerto
Rico, Culebra and St. Thomas. Moderate to fresh east to northeast
winds will continue at 10-15 knots with higher gusts at times increasing
to 15 to 20 knots over the weekend. Small craft advisory will remain
in effect overnight through Saturday for the offshore Atlantic waters.

&&

.MARINE...Across the regional waters, seas up to 7 feet will
continue across the Atlantic water and local passages. Winds will
remain from the east to east-northeast at 10 to 20 knots. For the
beach goers, there is a high risk of rip currents along the north
facing beaches of Puerto Rico and Culebra and along the north
facing beaches of Saint Thomas and Saint John.

&&

.PREV DISCUSSION... /issued 445 PM AST Fri Dec 15 2017/

SYNOPSIS...A mid to upper level ridge will hold across the forecast
area through the weekend and into early next week. Surface high pressure
ridge will continue to build and spread across the east central Atlantic
yielding moderate to strong east to northeast winds through the weekend.
Mostly fair weather skies and seasonal condtions expected to persist
for the next several days.

SHORT TERM...Today through Sunday...

The dominant high pressure ridge pattern, will continue to favor
a strong trade wind cap inversion across the region supporting
mostly fair weather skies across the islands. Model guidance,
satellite imagery and recent upper air sounding continued to suggest
a relatively dry and stable air mass to persist through Sunday.
In addition moisture advection will be limited except for that
brought in across the north and east coastal areas by the moderate
to strong east northeast trades. Expect plenty of sunshine and
few passing clouds with pleasant daytime and overnight temperaturesalong the north facing
beaches of Saint Thomas and Saint John.during the next few days.
Occasional light passing showers will remain possible during the
overnight and early morning hours followed by limited shower
activity during the afternoons.

LONG TERM...Monday through Saturday...

A mid to upper level ridge will hold across the forecast area through
at least Wednesday. The ridge pattern aloft is then expected to gradually
erode during the latter part of next week, as a polar trough will move
across the central Atlantic then sink southwards into the northeastern
Caribbean. The surface high pressure ridge pattern north of the region
is forecast to persist through the forecast period. This will result
in moderate to strong east northeast winds. Expect a fair and mainly
stable weather pattern across the islands and coastal waters through
most of next week, except for passing showers especially during the
early morning and late evening hours. Seasonable temperatures are
expected to continue. By the end of the period low level moisture
is forecast to gradually increase as the ridge aloft erodes in response
to an upper trough sinking southwards across the region. This will
result in a better chance for shower activity across the local islands.
Widespread and significant rainfall accumulations as not forecast
at this time.

AVIATION...VFR conditions will prevail across all terminals through
the forecast period. Afternoon SHRA over the SW quadrant of PR could
affect briefly TJPS/TJMZ. Winds will continue ENE at 10-15 kts with
higher gusts at times.

MARINE... A north swell between 4-6 feet will continue to affect
the Atlantic waters and passages overnight. This will result in a
high risk of rip currents across the Atlantic beaches of Puerto
Rico, Culebra and St. Thomas. Moderate to fresh east to northeast
winds will continue at 10-15 knots with higher gusts at times increasing
to 15 to 20 knots over the weekend. Small craft advisory will remain
in effect overnight through Saturday for the offshore Atlantic waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  76  85  77  84 /  20  20  30  30
STT  76  86  75  87 /  20  30  30  30

&&

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

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

AM...High Rip Current Risk through Saturday afternoon for Coastal
     Waters of Northern USVI and Culebra out 10 NM-Coastal
     Waters of Southern USVI Vieques and Eastern Puerto Rico out
     10 NM.

     Small Craft Advisory until 8 AM AST Saturday for Atlantic Waters
     of Puerto Rico and USVI from 10 NM to 19.5N.

&&

$$

SHORT TERM...JF
LONG TERM....RAM



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