Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 300850

Area Forecast Discussion
National Weather Service San Juan PR
450 AM AST Tue May 30 2017

.SYNOPSIS...A trough aloft will continue to interact with
moisture associated with a departing tropical wave to result
in periods of showers and thunderstorms today. The proximity
of this trough will continue to enhance afternoon showers and
thunderstorms Wed-Thu. A more seasonable weather pattern is
expected Fri-Sat with the next tropical wave passage on Sunday.


.SHORT TERM...Today through Thursday...

Abundant amounts of moisture trailing the tropical wave and the
instability aloft due to the lingering mid to upper level
trough/TUTT, continued to favor the development of showers and
isolated thunderstorms across the region during the overnight and
early morning hours. Expect these unstable conditions to continue
today, but with a slight break in cloudiness, shower and
thunderstorm activity by mid morning.

However, instability aloft and good moisture convergence along with
daytime heating will quickly give way to another round of afternoon
convection across the islands especially over the interior and west
sections of Puerto Rico. Showers and or isolated thunderstorms may
also form along the Yunque area then stream across the San Juan
metro area during the afternoon.

Expect the tropical wave to exit the region later today however
recent models guidance continued to suggest a TUTT low will
continue to develop and linger just north of the region through
Thursday. Although this feature will shift slowly eastward during
the period, Upper level divergence/diffluence associated with this
feature should persist over the northeastern Caribbean. This will
therefore maintain unstable conditions which in combination with
ample trade wind moisture transport and local effects, will
continue to enhance the development of showers/thunderstorms
across the regional waters and parts of the islands each day at
least through Thursday. The activity on Wednesday and Thursday
should however be less widespread as lesser moisture pooling is
expected due to somewhat drier air filtering from the east along
with a fine to moderate concentration of Saharan dust.


The aforementioned mid to upper level trough/TUTT low...which is
now located north of Hispaniola...will move eastward while
weakening with its associated axis crossing the local islands on
Friday. As this feature weakens Sat-Sun, a weak mid level ridge
pattern is expected to slowly build across Caribbean. At lower
levels, a tropical wave will reach the eastern Caribbean on
Sunday, bringing once again plenty of tropical moisture to the
forecast area. After the wave passage, a broad surface high
pressure across the central Atlantic will promote east southeast
winds Monday through much of the next work week.

Therefore, if the long term forecast holds, expect a seasonal
weather pattern Friday and Saturday with locally induced showers
and thunderstorms, followed by a wetter period on Sunday and early
Monday associated with a wave passage. Fair weather conditions
with warm to hot temperatures are expected next work week under
a mid level ridge pattern and east southeast winds.


.AVIATION...SHRA/ISOLD TSRA across the local flying til at least 30/12z.
This will result brief MVFR en route btw islands with VCSH or SHRA
at TJSJ/TJNR/TNCM/TKPK. Aft 30/16z...SHRA/ISOLD TSRA psbl at and
vcty TJMZ/TJBQ. Also, psbl MVFR at TJSJ due to isold streamer-
like SHRA/TSRA from el Yunque area. Latest TJSJ sounding indicated
ESE winds below FL050 at 10-22 kts. Sfc wnds lgt/vrb bcmg E-NE
10-15 kts at most terminals except for local sea breeze


.MARINE...Moisture associated with a departing tropical wave will
continue to result in periods of showers and thunderstorms today.
Seas are expected to remain at or below 6 feet and winds at 15-20
knots, particularly across the Caribbean waters. Mariners are
advice to exercise caution as winds and seas could be locally
higher in the vicinity of thunderstorms. There is a moderate risk
of rip currents across most of the local beaches.


SJU  87  79  86  79 /  40  20  40  40
STT  89  80  87  80 /  40  50  50  40




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