Area Forecast Discussion
Issued by NWS San Juan, PR

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725
FXCA62 TJSJ 230202
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1002 PM AST Tue Jan 22 2019

.UPDATE...
Trade wind showers were observed across the local waters, north
and east Puerto Rico. The remnants of a cold front stalled north
of the islands will continue to promote a northeasterly wind flow
between 15 and 20 mph with higher gusts, increasing at 20 to 25
tomorrow and Thursday. This flow will favor low level convergence
and moisture transport increasing the frequency of showers moving
across the waters into coastal areas of northern and eastern
Puerto Rico early Wednesday morning. This activity will then moved
into the interior and western sections late Wednesday morning into
the afternoon hours. Rainfall accumulations will remain minimal
due to a mid to upper level ridge and the expected rapid movement
of this showers.

&&

.AVIATION...
Trade wind showers could briefly affect TJSJ/TIST/TISX/TNCM/TKPK
at times. In general, VFR conditions expected to prevail across
all terminals through the forecast period. Surface winds will
continue E-ENE at 10 to 15 increasing at 15-25 kt and gusty after
23/13z.

&&

.MARINE...
No changes were made to the inherited marine forecast. Hazardous
marine conditions are forecast Wednesday through at least Saturday
morning. The risk of rip current will increase to high along the
Atlantic coastline of Puerto Rico and the U.S. Virgin Islands as
well as across some north facing beaches of St Croix and Vieques.
Dangerous breaking wave heights are forecast along the north and
northwest facing beaches of Puerto Rico and the U.S. Virgin
Islands. This breaking waves are forecast to peak between
Wednesday night and early early Thursday morning where minor
coastal beach erosion should not be ruled out.

&&

.PREV DISCUSSION... /issued 532 PM AST Tue Jan 22 2019/

SYNOPSIS...The proximity of a cold front and a pre-frontal trough
will bring showers to the local area and increasing winds tonight
through Wednesday night. Marine conditions will become
increasingly hazardous through Wednesday night. Showers will
continue as winds abate Thursday and Friday, then scattered
showers will result from patches of moisture in a more relaxed
easterly flow.

SHORT TERM...Tonight through Friday...
High pressure at the surface and in lower levels will drive into
the western Atlantic during the period followed by another cold
front. This will tighten the gradient considerably over the area
so that winds as low as 925 mb could reach 25 to 30 knots and will
boost the surface winds across the area. At this time sustained
winds are not expected to reach 25 mph except in local passes and
restrictions but gusts to 30 mph are quite likely Wednesday
through Thursday. Gradients will relax on Friday. Moisture from a
pre-frontal trough will continue over the area through the period
and the area around the front will also be quite moist at 850 mb.
The front is expected to move very close to the local outer waters
by Wednesday and then sag into the northeast corner as it slowly
dissipates Thursday through Friday. This will spread light to
moderate showers through the area, but especially in the Atlantic
waters and on the northeast coasts and slopes of Puerto Rico and
in the northern U.S. Virgin Islands.

At upper levels, a 60-80 knot jet will continue over the area
through the period from the west northwest wrapping around a high
centered over Venezuela.

At mid levels, although moisture intrudes into the mid levels
somewhat Wednesday through Friday, generally speaking mid levels
above around 12 kft are very dry throughout the period and will
limit rainfall amounts.

LONG TERM...Saturday through Tuesday...
Flow at lower levels shifts to a more easterly direction and
moisture becomes patchy Saturday through Tuesday over the local
area. As the surface high pressure moves away into the central
Atlantic the cold front that follows will stall farther away from
Puerto Rico and the U.S. Virgin Islands. With relaxed gradients
winds will also return to normal. This will leave variably cloudy
skies with scattered showers during the period--mostly in the
eastern two thirds of Puerto Rico. Accumulations will be mostly
light due to the shallow nature of the good moisture and the very
dry aspect of the mid layers through the period and beyond.

AVIATION...Mainly VFR conditions expected to prevail across all
terminals through the forecast period. However, trade wind showers
could briefly cause tempo MVFR cigs across the PR/USVI terminals.
Low level winds will continue E-ENE at 15-25 kt and increase to 15
to 30 knots aft 23/12Z. Maximum winds 65-75 knots btwn FL380-480.

MARINE...Northerly swell will peak late Wednesday night and east
northeast winds will begin to subside about the same time. Seas
will become hazardous during the next several days just about
everywhere in the forecast area, from the western side of Puerto
Rico which will experience up to 7 foot seas to the outer Atlantic
and nearshore waters of Puerto Rico and the north side of the
northern U.S. Virgin Islands whose seas will reach up to 12 feet.
Small craft advisories are expected to be down everywhere by the
end of Saturday if not sooner. A high surf advisory will likely be
needed on Wednesday night and continue until early Friday. The
high risk of rip currents will also spread to the exposed coasts
of Saint Croix and Vieques by Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  73  83  73  83 /  70  70  70  40
STT  73  85  73  83 /  50  70  70  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Friday afternoon for North Central-
     Northeast-Northwest-San Juan and Vicinity-Southeast-Western
     Interior.

     Small Craft Advisory from 2 PM Wednesday to 2 AM AST Friday for
     Southeast.

     High Rip Current Risk from Wednesday evening through Thursday
     afternoon for Vieques.

     High Rip Current Risk through late Friday night for Culebra.

     Small Craft Advisory from 8 PM Wednesday to 2 PM AST Thursday
     for Southwest.

     High Rip Current Risk from 6 AM AST Wednesday through Friday
     afternoon for Mayaguez and Vicinity.

VI...High Rip Current Risk through Friday afternoon for
     St.Thomas...St. John...and Adjacent Islands.

     Small Craft Advisory from 2 AM Wednesday to 8 AM AST Saturday
     for St.Thomas...St. John...and Adjacent Islands.

     High Rip Current Risk from Wednesday evening through Friday
     afternoon for St Croix.

AM...High Rip Current Risk through Friday afternoon 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 from 2 PM Wednesday to 2 AM AST Friday for
     Coastal Waters of Southern Puerto Rico out 10 NM.

     Small Craft Advisory from 2 AM Wednesday to 8 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-
     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 from 8 PM Wednesday to 2 AM AST Saturday
     for Coastal Waters of Southern USVI Vieques and Eastern
     Puerto Rico out 10 NM.

     Small Craft Advisory from 8 PM Wednesday to 2 PM AST Thursday
     for Coastal Waters OF Southwestern Puerto Rico out 10 NM.

     Small Craft Advisory from 2 PM Wednesday to 8 AM AST Saturday
     for Anegada Passage Southward to 17N.

     Small Craft Advisory from 2 AM Wednesday to 8 AM AST Friday for
     Coastal Waters OF Northwestern Puerto Rico out 10 NM.

&&

$$

SHORT TERM...CAM
LONG TERM....WS
AVIATION...CAM



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