Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 171942
AFDSJU

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

.SYNOPSIS...A very active tropical wave now moving across the forecast
area will continue to produce showers and thunderstorms across parts
of the islands and local waters during the rest of today and overnight.
A TUTT low will shift farther west of the forecast area overnight,as
an upper ridge will gradually build from the north through Saturday.
An area of low pressure east of the Lesser Antilles is expected to move
across the eastern Caribbean late Friday through Saturday. This will
increase the potential for squally conditions and thunderstorms mainly
across the Caribbean waters. The National Hurricane Center is issuing
advisories on this Potential Tropical Cyclone Nine and an Air Force
Reserve Hurricane Hunter aircraft is currently enroute to investigate
the disturbance.

&&

.SHORT TERM...Overnight through Saturday...The combination of the
tropical wave passing through the local area and the proximity of
the upper trough west of the region will maintain unstable weather
conditions over the forecast area overnight through early Friday.
Showers and thunderstorms over the islands should diminish by early
evening, but is expected to again redevelop across the coastal waters
and reach portions of PR and the USVI by early morning. Somewhat drier
conditions is expected by Friday afternoon as the Tropical wave will
have exited the region, and the upper level ridge gradually builds
over the area along with an intrusion of suspended Saharan dust
expected to move across the region. On Saturday The chance for showers
and thunderstorms will again increase as invest 91L/potential Tropical
cyclone nine moves south of the area and peripheral moisture is expected
to propagate northward and affect the forecast area.

.LONG TERM...Sunday through Friday...The area of low pressure Invest
92L, currently has a 60 percent chance of formation through the next
5 days. Based on recent info from the National Hurricane center, this
system is expected to encounter unfavorable upper level winds for further
development and should move northeast of the islands on Sunday as a
tropical wave. However, recent model guidance continued to suggest
that the overall layered precipitable water/moisture content will
remain high through the early part of next week. This should support
showers and isolated thunderstorm development each day across the
islands. Another tropical wave and Tutt low is forecast to approach
the local area by Tuesday. This should bring increased instability
and favorable conditions for enhanced convective development through
at least Wednesday. So far, a gradual improvement in the overall weather
pattern is expected across the region by Thursday and Friday.

&&

.AVIATION...BKN-OVC skies expected through the afternoon across the
terminals in PR while the USVI and TNCM/TKPK observes mainly FEW_SCT
clouds. CIGS across terminals in PR will be at Fl080 to about FL110.
Wx improving this afternoon and tonight. Winds will remain mainly
easterly at 10-15KT with occasional higher gusts for the rest of
today, decreasing winds tonight. Mainly VFR conds expected starting
this afternoon into Friday, winds increasing after 18/13Z at about
15KT from the east.

&&

.MARINE...Showers and isolated thunderstorms will affect parts of
the regional waters during the rest of the overnight hours, as the
tropical wave will continue to exit the region. Small craft advisories
will continue in effect across much 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.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  76  88  78  88 /  30  20  60  40
STT  75  92  80  89 /  20  20  50  50

&&

.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 6 PM AST Saturday 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 6 PM AST Saturday for Anegada Passage
     Southward to 17N-Atlantic Waters of Puerto Rico and USVI
     from 10 NM to 19.5N-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 from 2 AM to 6 PM AST Saturday for Coastal
     Waters of Northern Puerto Rico out 10 NM-Coastal Waters of
     Northern USVI and Culebra out 10 NM-Mona Passage Southward
     to 17N.

     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...JF
LONG TERM....RAM



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