National Weather Service San Juan PR
443 AM AST Thu Feb 11 2021
.SYNOPSIS...
A pattern of generally fair weather, with isolated to scattered
showers in a typical pattern, will continue over the next several
days. No significant rainfall accumulations are expected. A surface
high north of the region will persist as well, leading to brisk
winds over the region. Seas of up to 7 feet are possible today in
the offshore Atlantic waters, and a Small Craft Advisory is in
effect. There is a high risk of rip currents for beaches of
northwestern and north central Puerto Rico today.
&&
.SHORT TERM...Today through Saturday...
Satellite imagery shows an area with clouds and Total
Precipitable Water ranging between 1.0 and 1.3 inches over and
approaching the islands from the east. This air mass will promote
passing clouds and showers across the windward sections of
PR/USVI, and due to fast trades, they could reach further inland
across Puerto Rico at times. Showers will then spread into the
western portions of Puerto Rico and downwind from the U.S. Virgin
Islands by mid-morning and during the afternoon.
A mid-level ridge will promote a subsidence cap over the region,
which will inhibit organized convection. However, a surface-high
pressure near the Bahamas will slowly drift eastward into the
Atlantic Ocean through the weekend until the Azores High establishes
by Saturday. That said, surface winds will accelerate Friday and
Saturday and will veer from the east-southeast by the weekend. This
weather pattern will leave the islands under the influence of the
arrival of trade winds perturbations and the diurnal cycle during
the afternoons. At this time, Saturday seems the best day to have a
mixture of sunshine and clouds with little or no rain.
.LONG TERM...Sunday through Friday...
Much like yesterday, there has been very little in terms of change
with respect to the general pattern forecast through next week,
though some details remain in flux. A mid- to upper-level ridge will
continue to provide stability, and dry air, aloft; this will inhibit
convective development, and effectively prevent significant
organized convection throughout the period. In the upper-levels, a
weak trough will skim by the area to the north early in the week,
and then strengthen to our east and southeast through most of the
week next week; this will lead to additional subsidence aloft for
the region. Additionally, relatively dry air is expected to be the
dominant air mass over the region, with various patches of moisture
pushing across the area from time to time. This moisture will help
to support isolated to scattered showers, which will occur in a
typical pattern; on the whole, though, generally fair weather is
anticipated through the long-term period. Again.
Though there is a weakness in the mid-level ridge forecast for this
weekend, model guidance suggests that the moisture will be a major
limiting factor - in that there isn`t very much of it. The 0Z run of
the GFS suggests precipitable water values significantly below
seasonal normals; similarly, the ECMWF has below average moisture.
This is probably the biggest change from the previous forecast -
Sunday is not only no longer a prime candidate for one of the better
days for rain, it is among the drier days next week. The patchy
nature of the moisture does make details less confident, so this
forecast could also change over the next couple of days. Keeping in
mind the low confidence in details, the best days for rain look to
be Wednesday and Thursday, with stronger, larger patches of moisture
forecast to push across the forecast area. Even so, significant
rainfall amounts are unlikely, and hazardous conditions are not
presently anticipated. What showers do develop are likely to be
quick-moving, further limiting rainfall accumulation potential for
any one location. This is due to a surface ridge located north of
the area, which will persist in providing a tight pressure gradient
over the region, leading to brisk winds.
&&
.AVIATION...
VFR conditions will prevail thru the forecast period. The E-NE winds
will push clouds and ISOL-SCT rain (at times) in the VCTY/over
IST/JSJ/ISX/NCM/KPK. SCT-BKN between FL020-FL050 is possible at
times. Then, clouds and showers will develop over the interior/W-PR
between 11/15z-22z. No significant impacts to operations expected.
Winds will continue at less than 10 kt thru 11/13z, increasing at 15
to 20 kt with higher gusts.
&&
.MARINE...
Moderate to fresh winds will continue for the next several days,
causing building seas. Hazardous conditions are expected for the
offshore Atlantic waters. At Buoy 41043, located north of the
islands, seas of 7 to 7.5 feet have been observed. This evening,
hazardous conditions are forecast to spread, developing in the
Anegada Passage. Small Craft Advisories are in effect for both the
offshore Atlantic waters and the Anegada Passage. Additional
advisories may be needed later this week, as further increases in
seas are expected, in response to the persisting brisk winds.
For the beachgoers: There is a high risk of rip currents for north
central and northwest beaches of Puerto Rico. Most other beaches
have a moderate risk of rip currents today, except for some beaches
of south central and western Puerto Rico.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 83 72 85 74 / 50 50 50 50
STT 83 74 84 73 / 50 50 50 40