National Weather Service San Juan PR
517 AM AST Sat Dec 1 2018
.SYNOPSIS...A surface high pressure moving from the western
Atlantic into the central Atlantic, will push the remnants of a
frontal boundary across the region through early next week.
However, an upper level ridge over the central Caribbean will
keep stable conditions. A similar pattern is forecast for the
second part of next week with another surface front stalling north
of the area and another surface high promoting trade wind showers.
&&
.SHORT TERM...Today through Monday...
A weak upper level trough will pass through from the west northwest
tonight, while the center of a high pressure remains near Central
America. Then the high will move through or just south of Jamaica
and the flow over the local area will become northwest.
High pressure at the surface, north of Hispaniola, at 30 degrees
north and another over New York will join over the western Atlantic
and move east into the west central Atlantic Sunday and Monday. An
old frontal band, near 22 north, will slowly sag south while bubbles
of moisture move across in the trade wind flow generated by the high
pressure. This will create scattered showers in our typical pattern
of night and early morning showers across the U.S. Virgin Islands
and eastern Puerto Rico, followed by showers in western and interior
Puerto Rico during the afternoon. A band of drier air will cross
through the Leeward Islands late this afternoon and move quickly
through Puerto Rico overnight. Then a larger area of low level
moisture will move into the southeastern third of the forecast area
Sunday morning and generate showers in Puerto Rico Sunday afternoon.
Moisture continues Sunday night, when precipitable water peaks near
1.9 inches, but it fades on Monday. Although scattered showers will
continue Monday, amounts will generally be light. The atmosphere
will be more stable than usual with lifted indices of minus 1 to
minus 4.
.LONG TERM...Tuesday through Saturday...
Surface high pressure will move further into the central and
northeastern Atlantic. Promoting moderate to locally fresh trades
through at least late Tuesday night. Winds relax through midweek
while another surface front enters the western Atlantic and
stalls north of the region by the end of the workweek. A surface
high pressure behind the front will increase winds and trade wind
showers once again during the end of the long term period.
Showers are expected each afternoon over western Puerto Rico while
trade wind showers continue across the USVI and over northeast PR
during the night time and early morning hours.
&&
.AVIATION...Bubbles of moisture in ENE flow south of a cold front
just north of 21 N are moving through the area with -SHRA and LCL
MVFR CIGS. As the front appchs drier air will cause conds to improve
01/12-16Z. SHRA will re-dvlp in wrn PR with areas of mtn
obscurations and brief MVFR for TJMZ and psbly TJBQ btwn 01/17-23Z.
Sfc winds ENE 6-12 kt with sea breeze influences aft 01/14Z. Max
winds NW 25 kt at FL410, but winds 20 kt or less blo FL300.
&&
.MARINE...Northerly swell will keep seas between 5-7 feet across
the Atlantic waters through at least Monday. Therefore, a small
craft advisory is in effect for the offshore Atlantic waters due
to 7 ft seas. Elsewhere, seas will range between 4-6 feet and
small crafts should exercise caution through the rest of the
weekend. Moderate to locally fresh trades will continue for the
next several days. There is a high rip current risk in effect for
the northern beaches of PR, Culebra and St. Thomas through Monday
afternoon.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 87 74 85 75 / 50 40 40 50
STT 86 75 86 76 / 20 20 40 50