National Weather Service San Juan PR
436 AM AST Tue Jan 2 2018
.SYNOPSIS...A relative stable atmosphere will be in place until
late Wednesday, when a polar trough is forecast to amplify from
the west over the region. Low level winds will shift from east to
southeast in response to the aformentioned polar trough.
&&
.SHORT TERM...Today through Thursday... Low pressure at the surface
will begin to form just north of the Windward Passage tonight, then
spread north along the gulf stream, deepening rapidly. This will
break the ridge to our north and cause our winds to turn to the
southeast on Wednesday. Better moisture will also move across the
area behind a trough that crosses through Tuesday and Tuesday night.
This will enhance the shower activity beginning Wednesday afternoon
across most of the forecast area. Shower activity during the
afternoon will also shift away from the southwest quadrant of Puerto
Rico. Moisture values will peak midday Thursday although the best
moisture will not arrive until Friday. Flow aloft shifts to the
southwest today as the ridge over the area moves east of us.
Although some significant bands of divergence aloft pass through the
area they appear to do so during the parts of the day that
convection is not favored and hence most precipitation amounts will
remain limited and thunderstorms will remain improbable. The
southeast winds on Wednesday will allow some warming on the north
coast and in the Greater San Juan Metropolitan area. MOS guidance
seems to handle this well.
.LONG TERM...Friday through Wednesday...Computer models indicated
a frontal boundary and associated frontal trough will remain
across the southeastern Bahamas and northern Hispaniola Friday and
Saturday. However the proximity of these systems will induce a
moist southeast wind flow across the region. As a result, periods
of showers will be affecting the local region both days. For
Sunday through Wednesday next week, upper level ridge is forecast
to build north of the area. This will result in relatively fair
weather conditions across the northeast Caribbean throughout this
period.
&&
.AVIATION...VFR conditions will prevail through 03/06Z except for
brief MVFR conds psbl in wrn PR due to CIGS in SHRA. SHRA will
increase over PR aft 02/16Z--mainly over interior and western
sections. Hir trrn will be obscured till aft 03/02Z. Sfc winds will
be easterly 10 to 15 kt with sea breeze influences from 01/14-21Z
bcmg less than 10 kt overnight with land breezes. Max winds west 40-
50 kt from FL400-480 thru 03/06Z.
&&
.MARINE...Seas between 3 to 5 feet and winds up to 15 kts are
expected across the local waters, except across the Mona Passage,
where seas up to 6 feet can be expected. There is a moderate risk
of rip currents for the north coast of Puerto Rico, Culebra and
the eastern third of Vieques and some beaches on Saint Croix and
Saint Thomas.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 86 75 / 10 10 30 30
STT 84 74 84 74 / 20 20 30 30