Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 201512
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1112 AM AST Sun May 20 2018

.UPDATE...Sunny to partly cloudy skies prevailed during the
morning hours across the islands. By mid morning, streamers were
developing off the USVI, Culebra and Vieques and some low level
clouds were also developing over the mountain ranges of Puerto
Rico. Isolated to scattered showers are expected to develop across
these areas during the next few hours. The heaviest shower
activity is expected once again over western Puerto Rico, where an
isolated thunderstorm could develop during the afternoon hours.
Minor changes were made to the short term wind grids, however,
breezy conditions will continue across the coastal areas of the
islands and across the regional waters today.


&&


.AVIATION...Mainly VFR conditions are expected to prevail across
all the terminals. However, SHRA will develop over western PR
impacting mainly TJMZ and the VCTY of TJBQ. A brief isolated
thunderstorm is also possible across western PR. Elsewhere,
passing SHRA at times can not be ruled out. Latest 20/12z TJSJ
upper air sounding indicated east winds at 7-26 kts below FL100.


&&

.MARINE...Ponce and San Juan buoys were indicating seas at 5 and 6
feet respectively, and east winds around 20 knots with higher
gusts. The outer waters are expected to range between 6 to 8 feet
through at least Monday morning. Therefore, small craft advisories
continue in effect. A high rip current risk also continues through
at least Monday afternoon for the northwest coast of Puerto Rico.
There is a high risk today for the north coast of PR and St.
Croix.


&&

.PREV DISCUSSION... /issued 424 AM AST Sun May 20 2018/

SYNOPSIS...A persistent surface high pressure system remains to
the north of the region as a result moderate to fresh winds will
remain across the region along with brief passing showers. A TUTT
low positioned to the northeast of the Leewards Islands will move
way from the area by Wednesday and be replaced by ridging aloft.
Seasonable weather pattern is expected to prevail with showers
forming during the afternoon across northwest and western Puerto.

SHORT TERM...Today through Tuesday...Partly cloudy skies
prevailed across the forecast area overnight and early this
morning with frequent passing showers observed across the coastal
waters and the eastern sections of the local islands. However,
rainfall accumulations associated with these showers were minimal.
Temperatures were in the mid 70s at lower elevations under
easterly winds between 10 and 15 mph.

A mid to upper level trough (TUTT Low) will continue to meander across
the central Atlantic and into the northeastern Caribbean through the
forecast period. At lower levels, a board high pressure across the
central Atlantic will continue to yield brisk easterly winds early
this week. There is no major changes to the short term forecast due
to the lack of upper level forcing and moisture near or below the
normal range. As a result, continue to expect a seasonable weather
pattern with showers embedded in the trades at times as well as
showers and isolated thunderstorms developing in the afternoon
across western sectors of Puerto Rico each day. However, intensity
and areal coverage of showers should decrease Mon-Tue as low level
moisture decreases.

LONG TERM...Wednesday through Monday...The local area will remain
under the influence of a strong surface high pressure system. As a
result easterly winds of 10 to 20 kts with higher gusts as well as
showers embedded in the trade winds can be expected through
Monday. The TUTT low positioned to the northeast of the islands
will begin to move away from the area late Wednesday into
Thursday and will be replaced with ridging aloft through the
weekend. A seasonable weather pattern is expected to prevail with
brief passing showers. Model guidance depicts a TUTT low sinking
into the region again on Tuesday which could increase rain chances
across the islands.

Aviation...Mostly VFR conds at all TAF sites with VCSH likely in
and around JSJ/IST/ISX and Leeward terminals through the morning
hours. Aft 20/16z SHRA/TSRA expected across western Puerto Rico to
result in brief MVFR conds at JMZ and possibly JBQ through about
20/22z. Easterly winds 15 to 25 knots aft 20/12z with some sea
breeze variations.

MARINE...Today a small craft advisory is in effect for all
local waters ways due to seas of 8 feet and winds of 15 to 20 kts
with higher gusts. These hazardous conditions will prevail across
the area through Monday. A high rip current risk exist for the
northern and eastern beaches of Puerto Rico as well as the beaches
of Carambola, Salt River and Cramer Park that are in St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  75  86  76 /  30  20  40  40
STT  79  78  79  78 /  30  20  40  40

&&

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

VI...High Rip Current Risk through late tonight for St Croix.


AM...Small Craft Advisory until 8 PM AST this evening for Anegada
     Passage Southward to 17N-Coastal Waters OF Northwestern
     Puerto Rico out 10 NM-Coastal Waters of Northern USVI and
     Culebra out 10 NM-Coastal Waters of Southern Puerto Rico
     out 10 NM-Coastal Waters of Southern USVI Vieques and
     Eastern Puerto Rico out 10 NM.

     Small Craft Advisory until 8 AM AST Monday for Atlantic Waters
     of Puerto Rico and USVI from 10 NM to 19.5N-Caribbean
     Waters of Puerto Rico from 10 NM to 17N-Mona Passage
     Southward to 17N.

     Small Craft Advisory until 2 AM AST Monday for Coastal Waters of
     Northern Puerto Rico out 10 NM.

&&

$$

DS



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