Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 272059

Area Forecast Discussion
National Weather Service San Juan PR
459 PM AST Thu Jul 27 2017

.SYNOPSIS...TUTT low northeast will continue to weaken and move
into the Central Atlantic for the next few days. A tropical wave
is forecast to move across the area on Friday. A broad surface
high pressure will continue to hold over the central Atlantic.
Another tutt low is forecast to meander over the eastern Caribbean
through the weekend. A mid level ridge will build north of the
area and hold through mid week next week.


.SHORT TERM...Tonight through Saturday...
Fair weather conditions are expected to prevail through at least
Friday morning...when moisture associated to a tropical wave is
expected to increase across the USVI and through PR through Friday
evening. Therefore, scattered to locally numerous showers and
isolated thunderstorms are expected to develop across portions of
the islands during the afternoon. High resolution models suggest
higher rainfall amounts across the north central and northwestern
portions of PR during the afternoon hours. On Saturday-Sunday,
tutt low meandering just east of the islands is expected to
enhance shower activity with possible thunderstorms across the
Anegada Passage into the eastern waters of PR/USVI. Followed by
afternoon convection mainly over and west of the mountain ranges
of PR.

.LONG TERM from PREV DISCUSSION.../issued 515 AM AST Thu Jul 27
2017/...Sunday through Friday...

A weak mid level ridge is expected to hold across the area through
the forecast period. At lower levels, a broad high pressure across
the central Atlantic will continue to prevail, resulting in east to
east southeast winds through Tuesday. Precipitable water is expected
to remain near the normal range which is 1.75 inches through midweek.
Moisture advection and a fresh to locally strong east northeast wind
flow is expected Thu-Fri as an easterly disturbance moves across
the area.

Therefore continue to expect a seasonable weather pattern with trade
wind showers across the USVI and E PR at times, as well as showers
and thunderstorms developing across west sections of Puerto Rico in
the afternoon Sun-Tue. The chance for shower and thunder activity
will increase Wed and into the end of the forecast period.


.AVIATION...SHRA are expected to continue across TJSJ and TJBQ until
at least 27/22z. After 27/22z, mostly VFR conditions are expected
across the local flying area with VCSH across the Leeward, USVI and
TJSJ TAF sites. ESE winds of 10 to 15 mph will diminish after
27/23z to light/VRB, increasing again at 10 to 15 kt after 28/14z.


.MARINE...Buoys across the coastal waters of the islands were
indicating seas at less than 3 feet and easterly winds between
8-15 knots. A tropical wave located now east of the Leeward
islands is forecast to enter the regional waters by Friday morning.
This will result in an increase in showers and isolated thunderstorms
across the local waters. Seas and winds are forecast to increase
early next week.


SJU  79  92  79  90 /  20  40  20  40
STT  80  88  80  89 /  30  30  30  50




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