National Weather Service San Juan PR
445 AM AST Thu Jan 10 2019
.SYNOPSIS...A mid to upper level trough will provide some instability
through Friday to result in cloudiness and periods of scattered
to numerous showers across the local isles. A more seasonal weather
pattern is expected the upcoming weekend into early next week with
trade wind showers across the eastern coastal areas of Puerto Rico
and the outlying islands.
&&
.SHORT TERM...Today through Saturday...
A cold front over the western Atlantic is expected to stall north of
the area through Friday. Meanwhile, a surface high over the central
Atlantic will continue to loose influence over the region. Winds are
expected to decrease and a deep layer southerly wind flow will
prevail. A mid to upper level trough will provide some instability
through Friday and in combination with the available low level
moisture, will result in cloudiness with periods of scattered to
numerous showers over portions of the regional waters and across the
U.S. Virgin Islands and Puerto Rico. For this afternoon, light
steering south-southwest winds and sea breeze convergence over
northern PR should lead to shower development along the northern
slopes as well across the eastern sections of the islands.
Moisture is expected to peak from tonight through Friday morning and
periods of intermittent showers are possible across the USVI and the
eastern sections of PR. A more southeasterly wind flow is expected
on Friday afternoon and shower development is expected mainly over
the northwest quadrant of PR. A mid to upper level ridge is forecast
to build from the west on Saturday and moisture content is expected
to erode. A surface high pressure is also expected to build over the
western Atlantic and northeast trades will return across the region.
.LONG TERM...Sunday through Friday...
The mid to upper level ridge pattern will prevail much of the forecast
period across the local isles with a brief weakening anticipated
Wed-Thu as a deep mid to upper level trough moves across the
western Atlantic into the central Atlantic. At lower levels, a
moderate easterly wind flow will prevail Sunday into early next
week, becoming southeast by midweek as a frontal boundary approaches
from the west. Under the aforementioned pattern, trade wind
showers will prevail Sunday followed by fair weather Mon-Tue as a
drier airmass encompasses the forecast area.
There is a better chance for shower activity Wednesday and Thursday
as the ridge aloft erodes and the frontal boundary approaches
from the west. A more seasonal weather pattern with trade wind
showers will prevail Friday into the weekend. Pleasant temperature
to continue, particularly by the end of the forecast period.
&&
.AVIATION...Mainly VFR conditions are expected early in the forecast
period across all the terminals. SHRA and sct/bkn layers btw FL030-
FL250 are expected this afternoon and through the evening hours
across portions of the islands and the surrounding coastal waters.
Tempo MVFR conds are possible across the PR/USVI terminals with this
activity. Low level southerly winds are expected between 5-10 kt,
sea breeze variations expected at TJMZ/TJBQ/TJSJ after 14z.
&&
.MARINE...A light to gentle east southeast wind flow will prevail
across the local waters through Friday, becoming more easterly
during the weekend. Although seas are expected to subside
throughout the day, another northerly swell is forecast to move
into the local waters during the weekend. However, seas will
remain below SCA criteria.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 84 73 / 40 50 50 20
STT 83 72 83 72 / 50 50 50 30