Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 171617
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1217 PM AST Thu Aug 17 2017

.UPDATE...The combination of the tropical wave passing through the
local area and an upper trough just west northwest of the local
area caused very unstable weather conditions over the local
islands. Showers and thunderstorms affected the eastern half of
Puerto Rico all morning with some showers also affecting the USVI.
The rainfall totals over PR were in the 4-6 inch range across NE
PR and SE PR as well, which caused some flash flooding across
those areas. The rest of the eastern half of PR observed urban and
small stream flooding. The heavy rain has ended and light to
moderate rain remains, but cloudiness is covering the local area
and strong afternoon convection seems a bit less likely.

&&

.AVIATION...BKN-OVC skies expected through the day across the
terminals in PR while the USVI and TNCM/TKPK is starting to
observe a break in the clouds with SCT sky. CIGS across terminals
in PR will be at around Fl060 to about FL100. -RA at TJSJ and
TJPS though the afternoon, reaching TJBQ and TJMZ later in the
afternoon into tonight. Winds will remain mainly easterly at
10-15KT with occasional higher gusts. Wx improving tonight.

&&

.MARINE...Small craft advisories continue in effect across many of
the local waters due to winds of up to 20 knots and seas up to 8
feet. Moderate to high risk of rip currents across the local
islands today.

&&

.PREV DISCUSSION... /issued 530 AM AST Thu Aug 17 2017/

SYNOPSIS...A tropical wave moving across the forecast area
will continue to result in showers and thunderstorms today. TUTT
low will continue west of the forecast area through late tonight
as an upper ridge builds from the north through Saturday. An area
of low pressure about 500 miles east of the Lesser Antilles is
expected to move across the Caribbean Sea on Saturday. This will
increase the potential for gusty winds and thunderstorms across
the Caribbean waters.

SHORT TERM...Thursday through Saturday...

Unsettle weather conditions will continue to prevail throughout the
day as an upper level trough/TUTT low interacts with a tropical wave
moving across the local isles. The chance for showers and
thunderstorms -squally weather type- will continue to be high
particularly during the morning hours across the USVI and the
eastern half of Puerto Rico as well as the local waters. Shower and
thunder development across west Puerto Rico this afternoon will be
dependent on cloud cover. The potential for urban and small stream
flooding as well as strong gusty winds continues.

A mid to upper level ridge is expected to build across the forecast
area tonight, as the aformentioned trough aloft/TUTT low shifts
westward. However, the ridge pattern aloft is expected to be short-
lived as trofiness returns to the local isles on Sunday. Therefore,
as the tropical wave moves away later today and an upper level ridge
builds, a fair weather pattern is expected to prevail on Friday. The
chance for showers and thunderstorms will increase once again on
Saturday as invest 91L moves south of the area but peripheral
moisture reaches the forecast area. Based on the NHC forecast,
this area has a formation chance of 60 percent in the next 48
hours. Stay tuned.

LONG TERM...Sunday through Thursday...

Another area of low pressure, invest 92L, currently has a 50
percent chance of formation through the next 5 days. This system
however is expected to encounter unfavorable upper level winds
and move close or just to the northeast of the islands on Sunday
as a tropical wave. Overall, precipitable water content will
remain high through the first half of next week. As another
tropical wave is forecast to reach the local area on Tuesday.

AVIATION...MVFR or even IFR conds will remain possible at all TAF
sites in SHRA/TSRA as a tropical wave and associated moisture moves
across the area. ESE winds 15 to 20 knots with gusts around 35knots.
Wx conditions are expected to improve tonight.

MARINE...Hazardous seas will continue today across the regional
waters due to seas between 6-8 feet and easterly winds between
15-22 kts. Strong thunderstorms with frequent lightning and gusty
winds are expected today as a tropical wave continues to exit the
local area. There is a high rip current risk for beaches across
the north, east and south coast of PR and St. Croix. Hazardous
seas are expected once again on Saturday morning as a low pressure
area moves across the Caribbean Sea.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  88  76  88  78 / 100  20  20  40
STT  88  75  92  80 /  40  30  20  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for Central
     Interior-North Central-Northeast-Northwest-San Juan and
     Vicinity-Southeast-Western Interior.

VI...High Rip Current Risk until 6 PM AST this evening for St Croix.

     Small Craft Advisory until 2 PM AST Friday for St.Thomas...St.
     John...and Adjacent Islands.

AM...High Rip Current Risk until 6 PM AST this evening for Coastal
     Waters of Southern Puerto Rico out 10 NM.

     Small Craft Advisory until 2 PM AST Friday for Anegada Passage
     Southward to 17N-Caribbean Waters of Puerto Rico from 10 NM
     to 17N-Coastal Waters of Southern USVI Vieques and Eastern
     Puerto Rico out 10 NM.

     Small Craft Advisory until 2 AM AST Friday for Coastal Waters of
     Northern Puerto Rico out 10 NM.

     Small Craft Advisory until 6 AM AST Saturday for Atlantic Waters
     of Puerto Rico and USVI from 10 NM to 19.5N.

     Small Craft Advisory until 6 PM AST this evening for Coastal
     Waters of Northern USVI and Culebra out 10 NM-Mona Passage
     Southward to 17N.

&&

$$

SHORT TERM...JA
LONG TERM....WS



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