Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 281918
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
318 PM AST WED SEP 28 2016

.SYNOPSIS...Tropical Storm Matthew will pass about 300 miles south
of Puerto Rico on Thursday with moderate to fresh easterly winds
over the local islands and fast moving showers of heavy rain.
Showers will taper off Friday and Saturday, but showers with heavy
rain will return in southerly flow late Saturday into Sunday and
continue through much of next week.

At upper levels...An area of high pressure will move through the
area this afternoon through Friday with the low from TS Matthew
passing south of the local area on Thursday. Although low pressure
slants in from the northeast over the Windward Islands over the
weekend, high pressure dominates the area until mid week next
week.

At mid levels...A ridge of high pressure extending across
Hispaniola will drift west over the Bahama Islands tomorrow while
TS Matthew passes through the Caribbean to the south of the
forecast area. Weak troughing will continue over the local area
until midweek next week. The mid layers of the atmosphere will be
moist on Thursday and again Saturday night through at least
Wednesday.

At lower levels...TS Matthew will dominate most of the lower level
flow as it crosses westward through the eastern Caribbean Sea and
south of the U.S. Virgin Islands and Puerto Rico on Thursday. Then
southeast to south flow will prevail until late next week as
Matthew moves north across the Bahama Islands. Lower levels will
be moist through Sunday and relatively moist through the following
weekend.

&&

.DISCUSSION...Winds picked up early this morning but remained
generally below 20 knots in the local forecast area. The National
Hurricane Center named the tropical disturbance Tropical Storm
Matthew at 11 AM AST as it approached the Windward Islands around
13.4 north. Reports of 52 knot winds were returned by the
reconnaissance aircraft in its northeast quadrant. Meanwhile, back
in The U.S. Virgin Islands and Puerto Rico, showers shriveled
under Saharan dust and subsidence from the approaching system.
Showers and tropical storm force winds will invade the Caribbean
south of Puerto Rico tonight. Winds of 20 to 35 mph are expected
across the local waters tonight and tomorrow with some sustained
winds--up to 25 mph possible over land. The GFS is currently (in the
28/12z run) taking Matthew closer to Cabo Rojo than the current
track, but the GFS has shifted the track with every run.
Conditions will improve beginning Thursday night across the
forecast area and some drying will also take place Friday and
Saturday. But then the tail and principal moisture feed of Matthew
is expected to cross Puerto Rico and spill over in the the U.S.
Virgin Islands. This will make for a long episode of rainy wet
weather that could produce extensive flooding in the area if the
forecast track of TS Matthew holds close to its passage through
the Windward Passage and the Bahama Islands.


&&

.AVIATION...Mostly VFR conditions expected across the local
flying area until 28/19Z. After 28/19Z, SHRA and TSRA will begin
to affect TKPK and then TNCM producing periods of MVFR o even IFR
conditions. After 29/05Z, SHRA and TSRA will propagate across
TIST, TISX and TJSJ with periods of MVFR conditions. MVFR
conditions possible after 29/16 at TJPS, TJMZ and TJBQ with MTN
Top obscurations near convection along interior and west PR
between from until 29/22Z. Winds are expected to increase this
evening becoming from the East at 15 to 20 with gusts to 30kt
increasing to 20 to 30 kt with gusts to 40kt aft 29/12Z.


&&

.MARINE...Small craft advisories are already up over the eastern
portion of the marine waters and by Thursday morning all of the
marine forecast zones will see at least some portion of their area
with winds of at least 15 to 20 knots up to 32 knots and seas of
at least 10 feet and up to 15 feet or locally more. Conditions
should improve such that most or all zones will be free of small
craft advisories by Saturday afternoon. However showers and
thunderstorms will likely increase late Saturday night with heavy
rains on and off into much of next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  79  87  78  88 /  50  50  30  30
STT  79  89  79  88 /  60  60  40  40

&&

.SJU Watches/Warnings/Advisories...
PR...Small Craft Advisory from 8 AM Thursday to 6 AM AST Friday for
     Northeast-Southwest.

     Small Craft Advisory from 8 PM this evening to 6 PM AST Friday
     for Southeast.

VI...Small Craft Advisory until 6 AM AST Friday for St.Thomas...St.
     John.. and Adjacent Islands.

AM...Small Craft Advisory from 8 AM Thursday to 6 AM AST Friday for
     Coastal Waters OF Southwestern Puerto Rico out 10 NM.

     Small Craft Advisory until 2 PM AST Friday for Anegada Passage
     Southward to 17N.

     Small Craft Advisory from 8 PM this evening to 6 PM AST Friday
     for Coastal Waters of Northern Puerto Rico out 10 NM-
     Coastal Waters of Southern Puerto Rico out 10 NM.

     Small Craft Advisory until 6 AM AST Friday for Coastal Waters of
     Northern USVI and Culebra out 10 NM-Coastal Waters of
     Southern USVI Vieques and Eastern 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-Caribbean
     Waters of Puerto Rico from 10 NM to 17N.

     Small Craft Advisory from 8 PM this evening to 6 AM AST Saturday
     for Mona Passage Southward to 17N.

     Small Craft Advisory from 8 PM this evening to 6 AM AST Friday
     for Coastal Waters OF Northwestern Puerto Rico out 10 NM.

&&

$$

72/12


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