National Weather Service San Juan PR
508 AM AST Sun Mar 10 2019
.SYNOPSIS...A mid to upper level trough pattern is forecast to
remain northeast of the region through next week. Surface high
will build across the western Atlantic and promote an east to
northeast wind flow for the next several days. Moisture advection
and northeast steering flow will result in passing showers at
times across the Atlantic waters and over portions of the islands.
Diurnally induced shallow convection expected across the
interior/southwest sections of PR each afternoon. A weak frontal
boundary is forecast to move across the islands during the end of
the week.
&&
.SHORT TERM...Today through Tuesday...
Mostly clear skies prevailed across the local islands overnight and
early this morning. Passing showers were observed across the local
waters with a few of them affecting the local islands. However,
rainfall accumulations associated with these showers were minimal.
Winds were from the east 10 mph or less.
A mid to upper level trough is expected to amplify across the
northeast Caribbean with its associated axis relocating east of the
forecast area by Tuesday afternoon. Latest model guidance suggested
a minimum in precipitable water throughout the day today, followed
by a sharp increase tomorrow as the trough aloft and the east
northeast wind flow promotes moisture advection across the local
area. Moisture advection, however, is expected to be short-lived as
the trough axis relocates east of the area by Tuesday afternoon with
its convergent side dominating the local weather regime.
Under this evolving pattern expect fair weather conditions today
with some showers developing over southwest Puerto Rico in the
afternoon. The chance for shower activity is expected to increase
tomorrow with passing showers across the northern slopes of Puerto
Rico and USVI in the morning followed by shower activity across the
interior and southwest Puerto Rico in the afternoon. On Tuesday,
drier with limited shower activity. Showers if any will be focused
across the southwest PR in the afternoon.
.LONG TERM...Wednesday through Sunday...
A surface high pressure over the western Atlantic will push a weak
frontal boundary across the region during the end of the week.
Winds will decrease to 5-15 mph by midweek. A deep polar trough
is expected to replace to previous mid-upper level trough
northeast of the region. This will maintain an advective pattern
with showers streaming from the Atlantic waters across the islands
at times, however as the area remains under the convergent side of
the trough, drier air and fair weather conditions are expected to
prevail. The frontal boundary will increase the chances of rain
on Thursday and Friday, but only light to moderate rain is
expected at this moment. Drier air and a shallow moist layer is
expected during the weekend, promoting fair weather conditions
once again across the islands.
&&
.AVIATION...VFR conds are expected to prevail at all TAF sites
through the forecast period with VCSH possible at JMZ between
10/16z and 10/22z. Easterly winds 15 to 20 knots to continue.
&&
.MARINE...Surface high across the western Atlantic will maintain
moderate to locally fresh trade winds through early next week.
This will cause choppy seas up to 6 feet and winds between 15-20
kt, therefore small crafts are urged to exercise caution. A
moderate risk of rip currents will continue for most of the east,
north and southern beaches of the islands.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 84 74 83 73 / 20 30 50 50
STT 84 73 84 73 / 20 30 40 40