National Weather Service San Juan PR
502 AM AST Tue Feb 1 2022
.SYNOPSIS...Unsettled weather pattern will persist for the rest of
the week. This will increase the potential of shower and
thunderstorm activity across the islands. Seas will be the main
concern this week, due to a fading northwesterly swell that is in
our area and a second one arriving by late Tuesday, resulting in
hazardous marine and coastal conditions.
&&
.SHORT TERM...Today through Thursday...
A transition to more unsettled weather is expected to gradually
occur in the short term period, as the chances of rain and
thunderstorms increases with each passing day. An upper trough will
develop and become gradually stronger, its axis over Cuba on
Wednesday, but will continue to amplify and by Thursday it will be
positioned over Hispaniola, which is very favorable for instability
over the local area. In the mid levels, a similar pattern is
observed, but perhaps a bit further west on Thursday morning, but
approaching the local area by Thursday afternoon. This pattern will
cause an increase in the chances of thunderstorms. The available
moisture is also expected to increase gradually, but a narrow area
of drier air could be present over PR early on Wednesday. However,
late Wednesday into Thursday, the moisture will increase to above
normal levels.
Today appears to be the day with the most limited shower coverage,
with central into western and northwestern PR having scattered to
numerous showers and isolated thunderstorms in the forecast for this
afternoon. Wednesday and Thursday could have a more broad rainfall
coverage, though not necessarily very significant amounts of rain
on Wednesday, but widely scattered showers and isolated
thunderstorms are forecast. Thursday looks like the day where the
more significant showers over a more generalized area starts to take
shape, especially by Thursday night, where numerous showers and
isolated thunderstorms are forecast over the local waters, northern
PR and the USVI.
The winds today are expected to be on the lighter side, generally
around 10KT, but there will be a predominant wind flow from the
east, which will then cause sea breeze convergence across western
PR. This convergence and the expected orographic lifting from the
local effects will play a role in the development of the expected
shower and thunderstorm activity. Elsewhere, there is a slight
chance of showers based on the latest guidance. East to ENE winds at
10 to 15KT are expected over the local area for Wednesday and
Thursday, and the afternoon shower and thunderstorm activity over PR
would be over the central, western to southwestern sections.
However, the proximity of the aforementioned mid and upper level
troughs, as well as the moisture gradually increasing, will cause
shower and isolated thunderstorm activity over the local waters and
areas close to the USVI.
.LONG TERM...Friday through Wednesday...
Model guidance continues to suggest, for the most part, a wet and
unstable weather pattern for the first half of the long-term period.
GFS and ECMWF are consistent on the development of a mid- to upper-
level low and reflected surface induced trough across the northeast
Caribbean basin by the end of the workweek into the weekend. This
will maintain an unstable weather pattern across the area as 500
mb temperatures plummet and lapse rates get steeper across this
area. Combined with above-normal available moisture from remnants
of a frontal boundary, weather conditions could be conducive for
deep convective activity across the forecast area.
Uncertainty, however, still remains regarding the positioning of
the aforementioned trough, as stated in previous discussions. The
GFS Galvez-Davison Index continues to indicate enhanced moisture
convergence and the potential for scattered thunderstorm activity
capable of producing heavy rainfall across the CWA through at
least Sunday evening. Meanwhile, latest ECMWF run has backed off
from the above normal moisture content solution for this weekend
going back to a more modest activity over land areas and leaving
the most active part over the Atlantic waters. Therefore, forecast
confidence regarding specific impacts related to the weather
pattern for Friday through this weekend continues to be low as
trough placement and moisture availability continues to change
between model cycles. Please continue to monitor our forecast as
we follow the evolution of this event with the potential for
flooding impacts across the local region.
By early next week, a gradual transition into a more seasonal
weather pattern will take place. A building ridge at mid levels will
promote dry air intrusion aloft. Therefore, mainly fair weather
conditions can be expected with isolated to scattered showers
over western Puerto Rico each afternoon and passing showers
across the eastern third of Puerto Rico and USVI during overnight
and morning hours. Isolated thunderstorms could still be possible
as we transition to a more dry weather pattern by Wednesday.
&&
.AVIATION...
VFR conditions expected across the local TAF sites through the
forecast period. ISOL showers across local flying area, may cause
brief VCSH at the TIST and TISX terminals through the day. VCSH is
also possible at TJSJ in the morning, then TJBQ may observe VCTS
after 01/17Z. Winds of 10KT to 15KT are expected with a sea breeze
variations in PR, but E winds up to 10KT expected across the USVI
today.
&&
MARINE...A fading northwest swell will maintain seas up to 7 feet
through this afternoon for the Atlantic waters. Small Craft and
high Surf Advisories are in effect until this afternoon. Life-
threatening rip currents across the islands will persist for the
next several days.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 84 72 / 30 30 20 30
STT 80 75 80 75 / 20 20 20 40