National Weather Service San Juan PR
437 AM AST Thu Mar 17 2022
.SYNOPSIS...A generally stable weather pattern with breezy
conditions will prevail through the end of the workweek into the
weekend. At times, patches of low-level moisture embedded in the
trade winds will bring isolated to scattered shower activity and
support afternoon shower development, but rainfall accumulations
should be minimal. Lack of wetting rains will further dry soils
and fuels, leading to a threat of wildfires, mainly across
southern Puerto Rico. Moderate to fresh winds and a weak small
northerly swell will maintain choppy to hazardous marine and surf
zone conditions.
&&
.SHORT TERM...Today through Saturday....
Easterly winds, generally around 10 mph overnight, and up to 20 mph
during the day with occasional gusts are expected through the short
term period due to a surface high pressure that will remain near the
north central Atlantic as it slowly moves east. The mid to upper
levels are fairly stable, as a ridge of high pressure will prevail
over the local area. The available moisture will remain near to
below normal through the short term period. The precipitable water
will be below normal today, but will increase to near normal on
Friday. However, on Saturday, the precipitable water will be below
normal over the local islands, but it will be above normal over the
nearby waters. Therefore, generally brief isolated to scattered
showers are expected in the overnight and in the morning hours
across the USVI, and northern and eastern PR today and on Friday,
though perhaps more widely scattered over the local waters on
Saturday. Scattered showers are expected this afternoon across the
northwestern quadrant of PR. Sea breeze convergence could contribute
to the expected shower development, but the activity is not expected
to cause significant flooding, though ponding of water in poor
drainage areas will not be ruled out. The latest guidance suggests a
relatively stable day on Friday, with morning showers across eastern
PR, but little to no rainfall during the rest of the day over the
local islands. Even though we will have near normal moisture, the
drier air will start to filter by the late morning into the early
afternoon, and the dry air advection could limit the afternoon
shower activity. On Saturday, most of the shower activity is
expected to occur across the local waters, and little to no shower
activity over land areas.
.LONG TERM...Sunday through Thursday...
The most recent model guidance suggests a relatively drier weather
pattern, with model-estimated precipitable water vapor values of
1.2 inches or below prevailing during the long-term forecast
period. In this new solution, the strong polar trough and the
remnants of an old frontal boundary should remain well to the
north of the Caribbean region, having minimal impacts over the
area. If anything, a slight weakening of the mid-level ridge due
to the trough`s proximity and increased low-level moisture, with
the highest model-estimated precipitable water values of around
1.5 inches suggested for the cycle, could increase the potential
for showers on Monday. Even on the driest days, showers will favor
a seasonal advective pattern, dominated by overnight/early morning
showers moving over eastern Puerto Rico and the US Virgin Islands
at times. Afternoon convection will be limited to portions of the
interior and far western Puerto Rico through the cycle, with the
best chance for modest rainfall accumulations (around 0.25 inches
and possibly locally higher) on Monday. Nonetheless, the flood
threat will remain low. In contrast, the wind threat will remain
moderate, with the general wind flow exceeding 20 mph with higher
gusts through most of the cycle.
&&
.AVIATION...Mainly VFR conditions will prevail through the forecast
period. VCSH will affect TJSJ, TIST, and TJBQ until 17/14Z, but will
gradually increase up to around 20KT with to around 25KT thereafter.
Another round of showers would affect areas in and around TJBQ after
17/17Z, with VCSH likely and possible brief SHRA at the terminal,
which could cause TEMPO MVFR conds at some point between 17/17Z and
17/21Z.
&&
.MARINE...Moderate to fresh winds up to 20 knots and a weak small
northerly swell will maintain choppy to hazardous marine
conditions across most local waters, except coastal waters of
northern, southern, and western Puerto Rico. As a result, Small
Craft Advisories remain in effect. For beachgoers, a high risk of
rip currents also continues for beaches across the northwest to
northeast and southeast coast of Puerto Rico and most beaches of
Vieques, Culebra, and the US Virgin Islands.
&&
.FIRE WEATHER...Lack of wetting rains will further dry soils and
fuels across southern Puerto Rico, where KBDI values remain well
above 700, and 10-hour fuel moisture have ranged in the 9-10
percent in recent days. Satellite imagery indicated pockets of
drier air, with satellite-estimated precipitable water values as
low as 0.90 inches, approaching the region from the east. The
timing of these patches will be critical, causing relative
humidity values to fall into the lower-to-mid 40s during peak late
morning and early afternoon hours. At the same time, brisk
easterly winds will also affect the area, with local effects and
sea breeze variations causing winds to peak at 15-20 mph with
higher gusts. Given the expected weather conditions and current
state of soils and fuels, an elevated threat of wildfires is
anticipated, mainly across the southeastern coastal plains of
Puerto Rico. For this reason, a Fire Danger Statement has been
issued.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 87 75 87 75 / 30 40 30 10
STT 85 73 85 74 / 30 30 20 20