Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 231954

Area Forecast Discussion
National Weather Service San Juan PR
354 PM AST Fri Jun 23 2017

.SYNOPSIS...Mid to upper level high pressure ridge will hold across
the region though the weekend. Surface High pressure will remain anchored
across the west and central Atlantic through the weekend to maintain
moderate east to southeast trade winds. However, The chance for showers
and thunderstorms will increase across the region late Sunday and Monday
as a tropical wave is forecast to enter and move across the eastern


.SHORT TERM...Rest of today through Sunday...

Ridge pattern aloft will dominate the local weather conditions over
the next few days to maintain overall stable conditions across the
region. Limited moisture availability and subsidence aloft will inhibit
significant development of showers and thunderstorms across the islands
through at least Sunday. However...there will be sufficient moisture
convergence and diurnal effects to allow for afternoon convection
today and over the weekend. Showers and isolated thunderstorms
will remain possible mainly over parts of the interior and west
sections of Puerto Rico, as well as in and around parts of the San
Juan metro area, where streamer-like showers will be likely. The
remainder of the islands should experience mostly sunny skies with
only a few afternoon showers mainly on the downwind side of the

The prevailing easterly winds will continue to transport patches
of low level moisture across the region and bring a few showers
to the windward side of the islands...especially overnight and
during the early morning hours. Winds are expected to become more
southeasterly by Saturday, when afternoon showers should be
focused over northwest PR. For Sunday...conditions should be
somewhat drier ahead of the tropical wave expected on Monday, but
will not rule out the chance of afternoon showers.

.LONG TERM...Monday through Saturday...

Increasing moisture with showers and thunderstorm activity is expected
on Monday, as a tropical wave will enter and move across the eastern
Caribbean. This feature is expected to interact with a mid to upper
level trough/Tutt which will relocate just northeast of the
islands. As a result expect periods of enhanced convection across
portions of the islands and coastal waters through Monday. This
will be followed by a gradual decrease in shower activity on
Tuesday and Wednesday. Another tropical wave is forecast to reach
the forecast area on Thursday. This feature will again increase
local moisture convergence which should then persist across the
forecast area through Saturday. Good moisture convergence and the
proximity of a Tutt Low will therefore maintain a moist and
unstable weather pattern during the latter part of next week
through Saturday. Stay tuned as we will continue to monitor and
see how this pattern unfolds.


.AVIATION...VFR conds entire fcst prd. However, VCSH expected
across the local terminals at times durg the rest of the afternoon
and overnight. Some SHRA vcty of TJMZ/TJSJ and TJNR with brief
MVFR in SHRA psbl til 23/22Z...bcmg VFR across entire flying area.
Wnds fm E-NE at 10-15KT with occasional gusts...bcmg mostly LGT/VRB
aft 23z, then increasing once again 10-15 kts aft 24/14Z. No sig
operational wx impacts attm...except for the diurnally induced
aftn convection mainly ovr central and W PR.


.MARINE...Small craft should exercise caution across the nearshore
Atlantic,Caribbean waters and local passages due to winds up to 20
knots. The rest of the local waters can expect winds up to 15 knots
and seas up to 5 feet. There is a moderate risk of rip currents.
The next tropical wave is expected affect the regional waters
late Sunday through Monday. This will increase the chance for
showers and thunderstorms with areas of locally heavy rainfall and
gusty winds across portions of the local waters.


SJU  77  90  77  88 /  40  40  30  30
STT  78  89  79  90 /  40  40  30  30




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