Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 080059

Area Forecast Discussion
National Weather Service San Juan PR
859 PM AST Sun Mar 7 2021


Mostly fair weather prevailed over all the forecast area, a few
quick passing showers were observed over western sections of
Puerto Rico in the late afternoon hours. These weather conditions
will continue for the overnight hours. A few passing showers could
be possible over eastern coastal sections of Puerto Rico and the
U.S. Virgin Islands in the morning hours. However, not significant
rainfall accumulations are expected with this activity. A change
in wind direction is forecast tomorrow afternoon, more to the
northeast. As a result, afternoon shower activity, if any, to
southwestern sections of Puerto Rico.


Mainly VFR conditions are expected for all the TAF sites during
the next 24 hours. Winds are expected to maintain between VRB to
E-NE at 5-13 kts.



Relative tranquil marine conditions are expected with seas up to
5 feet and winds at 15 knots or less over the nearshore waters. In
the Atlantic offshore waters choppy marine conditions will
continue with seas up to 6 feet. Therefore, small craft should
exercise caution. For the beachgoers, there is a moderate risk of
rip currents across northern sections of Puerto Rico, all the
eastern beaches of Vieques and Culebra, as well eastern tip of St.


.PREV DISCUSSION... /issued 500 PM AST Sun Mar 7 2021/

SYNOPSIS...Fair weather conditions expected tonight and early
Monday. Winds turn from the east to northeast during the first
part of the week. A weak induced surface trough will increase
moisture content early in the week. A northerly swell will cause
hazardous seas starting on Tuesday.

SHORT TERM...Today through Tuesday...

A surface high pressure over the central Atlantic and a cold front
over the western Atlantic will maintain an east to southeast wind
flow through at least tonight across the region. In addition, a
mid-level ridge will continue to promote drier above 700 mb
tonight. Therefore, fair weather conditions should continue
through at least Monday monday morning across the islands. On
Monday, a pre-frontal trough is expected to develop mainly north
of the area as the cold front moves closer, this will cause winds
to turn from the northeast through the short term period. Therefore,
less warmer temperatures are expected during the first part of the
workweek. Due to the northeasterly steering winds and small surges
in low-level moisture, diurnally induced afternoon showers are
expected to develop each day over the southwestern quadrant of
Puerto Rico. During the night time, a cool advective pattern will
promote shower activity across the USVI and over the north and
east sections of PR.

LONG TERM...Wednesday through Sunday.../from prev discussion

An old cold front will linger north of the islands, promoting
moisture pooling over the region on Wednesday. The frontal
boundary will linger off to the north until it dissipated or
lifted away from the northeast Caribbean. Behind the front, a
surface high-pressure will move eastward across the western
Atlantic and will build across the central Atlantic throughout the
week. This high-pressure will increase local winds Wednesday and
Thursday, diminishing Friday into the weekend.

On the other hand, an amplifying mid to upper-level trough over
Cuba/Jamaica will approach PR/USVI weakening the ridge aloft. It
will cross the western Caribbean until its axis re-locate near the
Hispaniola by the second part of the week. They are some
discrepancy between the solutions of GFS and ECMWF. However,
they are consistently indicating an unstable weather pattern
Thursday through Sunday.

AVIATION...VFR cond thru prd. Mstly isold SHRA ovr regional waters
and en route btw islands. Isold-SCT SHRA psbl ovr NW PR and VCTY of
TJMZ/TJBQ til 07/22Z but no wx impacts fcst for local terminals at
this time. Winds mainly FM SE at 10 to 15 kts with some sea breeze
variations and briefly higher gusts...then bcmg calm to light and
variable aft 07/22Z.

MARINE...A northerly swell will move across the Atlantic waters
and passages on Tuesday. Moderate to fresh northeast trades will
also return during the first part of the week, causing choppy
conditions across the regional waters. Therefore, hazardous seas
are expected during this time and Small Craft Advisories will be
in effect due to seas greater than 7 feet. The swell will cause a
high risk of rip currents across most of the north facing beaches
of the islands from Tuesday through the end of the week.


SJU  75  86  74  84 /  20  20  30  50
STT  74  85  72  84 /  40  40  20  50




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