Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 270905
Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Mon Feb 27 2017
.SYNOPSIS...Bands of showers will pass through the area in
increasing trade wind flow. Showers will taper off as moisture
diminishes through Friday, but high pressure will drive moderate
to fresh trade winds through the week.
At upper levels...A ridge over the central Caribbean will weaken
and then shift to the western Caribbean by mid week. A trough will
deepen and sharpen over the area on Wednesday and move into the
tropical Atlantic by Thursday. A weak ridge will over the area on
Friday leaving high pressure over most of northern South America
and west northwest flow over the local area.
At mid levels...High pressure will continue across the Greater
Antilles and north of Puerto Rico through Saturday. The ridge then
shifts south through the areas on Sunday.
At lower levels...High pressure moved into the western Atlantic
this morning and will build slightly as it moves north of the
local area east of Virginia. Then it will diminish somewhat and
move into the central Atlantic by Friday. A second high will leave
the east coast of the United States on Sunday. These highs will
keep moderate to fresh trade wind flow mostly from the east
northeast. Bands of moisture will pass through the area Monday and
Tuesday. Areas of moisture will pass over the local area south of
a front late in the week and over the upcoming weekend.
.DISCUSSION...Bands of convection some with tops over 15 kft, have
passed through the area leaving amounts up to four tenths of an
inch in northeastern Puerto Rico. San Juan has had 16 hundredths
since midnight. Showers will continue through mid morning while
tapering off, then return overnight tonight for another round.
Accumulations will be light. Although isolated showers will occur
Wednesday through Friday better moisture will not occur until the
weekend. Cold fronts are tending to remain well north of the area,
but are still fostering some upward vertical motion between the
tropical air south of the area and the front over the weekend.
High pressure aloft is tending to keep mid levels relatively dry
.AVIATION...Mostly VFR conds are expected at all TAF sites with
brief MVFR conds possible early this morning in and around
JSJ/IST/ISX and the Leeward terminals in brief passing showers.
SHRA development likely aft 27/16z across SW PR, and this may
result in VCSH at JMZ through 27/22z. Easterly winds around 15
knots and sea breeze variations expected today.
.MARINE...Winds increase today through Wednesday and seas become
rough and hazardous beginning early tonight. Small craft
advisories will remain up in the outer Atlantic waters at least
through Friday, but this time the Caribbean waters will also be
affected as seas will be mostly wind driven. Some north swell will
however be present during the week adding some confusion to the
seas in the Atlantic and passages. Winds will exceed 22 knots at
times over the local waters mid week.
.PRELIMINARY POINT TEMPS/POPS...
SJU 84 76 85 76 / 60 30 40 20
STT 85 75 85 75 / 60 30 40 20
PR...VI...Small Craft Advisory from 8 AM Tuesday to 2 AM AST Friday for
St.Thomas...St. John.. and Adjacent Islands.
AM...Small Craft Advisory from 8 PM this evening to 8 PM AST Friday
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-Mona Passage Southward to
Small Craft Advisory from 8 PM this evening to 2 AM AST Friday
for Coastal Waters of Southern USVI Vieques and Eastern
Puerto Rico out 10 NM.
Small Craft Advisory from 8 AM Tuesday to 2 PM AST Thursday for
Coastal Waters of Northern Puerto Rico out 10 NM.
Small Craft Advisory from 8 PM this evening to 2 AM AST Thursday
for Coastal Waters of Northern USVI and Culebra out 10 NM.