Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 271752

Area Forecast Discussion
National Weather Service San Juan PR
152 PM AST TUE SEP 27 2016

.SYNOPSIS...A mid level ridge will remain across the region until
at least Thursday. An upper level trough will remain across the
forecast area until Wednesday. A surface high pressure north of
the region will continue to promote a moderate easterly wind flow
through Wednesday. A low pressure area associated with a tropical
disturbance about 400 miles east-southeast of the Windward
Islands will continue to move westward to west-northwestward near
20 mph tonight. Weather conditions during the second part of the
week and into early next week will be highly dependent on this
area of low pressure.


.DISCUSSION...Doppler radar indicated scattered to numerous
showers and isolated thunderstorms mostly across the Caribbean
waters late in the morning and early in the afternoon. This
moisture in combination with daytime heating and local effects
produced the development of showers and thunderstorms along, west
and north of Cordillera Central so far this afternoon. This
activity will continue to develop until the late afternoon and
early evening hours. Soils are already saturated across the
western interior of Puerto Rico, therefore any period of heavy
rainfall will likely result in urban flooding as well as sharp
rises along small stream and rivers with the potential for
mudslides in areas of steep terrain later this afternoon and this
evening. Maximum temperatures so far this afternoon ranged from
the upper 80s to the lower 90s degrees.

From Thursday into early next week the weather conditions across
the local islands will be highly dependent on the path of the
Invest 97L, located this afternoon at about 400 miles to the east
of the Windward Islands. Based on the latest Tropical Weather
Outlook issued by the NHC, this feature continues to show signs
of organization, and a tropical cyclone could be forming tonight
or early Wednesday, while the system moves west-northwestward at
about 20 mph. An Air Force Reserve reconnaissance aircraft is
on route to investigate the disturbance at this moment.

Regardless of development, marine conditions will quickly
deteriorate late Wednesday and Thursday...mainly across the
offshore Caribbean waters...with squally weather conditions
possible across water and land areas on Thursday. Beyond this,
models diverge, but overall as this feature moves into the
southwestern Atlantic the upcoming weekend and early next week,
tropical moisture will be advected across the area Sunday through
Tuesday. Therefore unsettled weather conditions possible Sun-Tue
with an increasing potential for flooding. We will continue to
monitor this situation. Stay tuned.


.AVIATION...MVFR conditions possible at TJMZ/TJBQ with MTN Top
obscurations near convection along interior and west PR between
until 27/22Z. SFC wnds will become mainly VRB05KT overnight and
easterly at 10-15 kts after 28/14z except for local sea breeze


.MARINE...Marine conditions will quickly deteriorate Wednesday
night and into Friday, as a tropical depression or a tropical
cyclone moves south of the area on Thursday. Small craft
advisories are in effect for most of the coastal waters starting


SJU  78  90  78  89 /  80  20  40  40
STT  81  90  79  88 /  30  20  50  50


.SJU Watches/Warnings/Advisories...


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