National Weather Service San Juan PR
446 AM AST Wed Dec 13 2023
.SYNOPSIS...
Issued at 439 AM AST Wed Dec 13 2023
The interaction of a surface high-pressure north of the area and a
strong low-pressure system northeast of the Caribbean will
continue to promote windy conditions over the local area.
Therefore, a Wind Advisory remains in effect until Thursday with
winds peaking today. Sustained winds at 20 to 30 mph with frequent
gusts around 35 to 45 mph are expected. Outdoor unsecured objects
could blow around or be damaged. Extremely dangerous marine and
coastal conditions through at least this weekend.
&&
.SHORT TERM...Today through Friday...
Skies were mostly clear over west and southwest Puerto Rico and
variably cloudy elsewhere and as passing clouds and light to
moderate showers reached the most of the islands from time to time.
The strong east northeast winds continued to steer patches of trade
wind moisture with embedded showers across the coastal waters and
inland mainly over the north and east sections of the islands. So
far the rainfall was of short duration with accumulations between
0.25-0.50 inches with the heaviest rains. Low temperatures ranged
from the mid to upper 70s along coastal areas and in the low to mid
60s in higher elevations and valleys. Surface winds were from the
east to northeast between 5 to 10 mph but with brief gusty winds
between 18-25 mph accompanied the passing showers.
The intervals of passing showers will continue to affect local
waters and mainly the north and east sections during the rest of the
morning hours. Expect a mixture of sunshine and clouds across the
region with breezy to windy conditions forecast through at least
Thursday. Showers are expected to move in and out of the area
steered by the strong east northeast winds, as the local pressure
gradient further tightens across the region due to the building high
pressure north of the region. Consequently strong sustained winds
winds between 20-25 mph is forecast along with frequent gusts
between 35 to 40 mph. As a result loose and unsecured small objects
may be blown around as well as hazardous driving conditions. For
this reason a wind advisory has been issued (NPWSJU) and will be in
effect at least until 9AM AST Thursday.
Afternoon clouds and shower development is expected to continue to
move inland and develop over portions of the interior and southwest
sections of Puerto Rico, as well as around the U.S. Virgin islands
and surrounding islands. However, as previously mentioned this
activity is expected to move quickly across the islands bringing
periods of sunshine and fair weather throughout the day. A similar
weather pattern is forecast for Thursday, with a mix of sunshine and
clouds and passing showers and pleasant near normal daytime and
overnight low temperatures. Breezy conditions are expected to
continue. By Friday, a wetter pattern is expected as the mid to
upper level ridge is to erode in response to a polar trough moving
across the west and southwest Atlantic. The east northeast wind flow
is also to become more easterly resulting in a return of remnant
trade wind low level moisture and convergence across the islands.
This along with the proximity of the mid to upper level trough will
aid in enhancing overnight and daytime shower activity while
increasing the chance for higher rainfall amounts, and the best
chance for ponding of water on road and poor drainage areas and
minor urban flooding in isolated areas. Widespread rainfall
accumulations are not anticipated at this time. The local trade
winds are also expected to relax across the region by Friday.
&&
.LONG TERM...Saturday through Wednesday...
The synoptic features influencing the long-term forecast have
remained relatively consistent, with the main alteration being the
timing of their effects. Above-normal moisture levels are expected
to persist on Saturday but are anticipated to decrease by Sunday,
remaining at near-normal levels. Ridging aloft will keep 500 mb
temperatures relatively warmer than the climatological normal with
250 mb height fields higher than usual. Consequently, the
atmospheric dynamics do not appear conducive for deep convective
development. However, despite this, there will be enough moisture
for shallow convective activity, leading to showery weather reaching
windward coastal sections during late evenings and morning hours,
especially on Saturday. Breezy wind conditions will continue, but
they are anticipated to be considerably less pronounced compared to
the short-term forecast.
The remainder of the long-term forecast will depend on a
strengthening area of low pressure that models continue to develop
over the south to southeast Gulf of Mexico. According to model
guidance, this robust low-pressure system is expected to move across
Florida by the upcoming weekend and then progress northward over the
western Atlantic. As this occurs, an elongated frontal boundary
associated with the low-pressure system is projected to envelop
the local area by early next week, with Tuesday anticipated to be
the wettest day in the long-term forecast.
This scenario will lead to southerly winds drawing abundant columnar
moisture, fostering increased moisture convergence across the
northeastern Caribbean. Additionally, atmospheric conditions aloft
appear to become conducive for deep convection. However, it's
crucial to note that the timing and positioning of these features
remain subject to change with varying models and each subsequent
model cycle, which have not been consistent in the last day or so.
Despite this inconsistency, there is an indication that the latter
portion of the long-term forecast, which corresponds to mid-week of
next week, will transition towards a more unsettled and wet
weather pattern.
&&
.AVIATION...
(06Z TAFS)
Issued at 439 AM AST Wed Dec 13 2023
VFR conds at all TAF sites. Brief MVFR conds psbl due to low passing
clouds with wdly SCT SHRA ovr regional waters and en route btw the
islands. SCT ocnl Bkn lyrs nr FL025...FL040. VCSH/-RA at TJSJ/TISX/
TIST and TJBQ til 12/13Z with mtn top obscr psbl ovr E interior of
PR due low cig/-RA. Low/lvl wnds fm ENE 25-30 kts BLO FL180...then
backing bcmg fm N and incr w/ht ABV. SFC wnd fm E-NE 5-10 kts bcmg
fm ENE 20 to 25 knots with gusty winds to 30-35 knots psbl aft
13/14Z.
&&
.MARINE...
Issued at 439 AM AST Wed Dec 13 2023
Nearshore Atlantic buoys are already observing seas of 7 to 8 feet
with wind speeds of 15 to 20 knots and higher gusts. This pattern is
expected to increase throughout the day with rough seas increasing
up to 12 feet and occasionally higher across Atlantic coastal
waters, and much higher for the offshore Atlantic waters. East to
east-northeast winds will also increase up to 25 knots with gusts up
to 45 knots. Therefore, Small Craft Advisories are in effect through
at least Saturday. Please refer to the latest Marine Weather Message
(MWWSJU) for more information.
&&
.SURF ZONE...
Issued at 439 AM AST Wed Dec 13 2023
Life-threatening rip currents due to rough surf and large breaking
waves. Nearshore buoys indicated that estimates of breaking waves
are already ranging between 9 to 11 feet. Therefore, a High Surf
Advisory is in effect for all surf zones across northern and eastern
Puerto Rico, Culebra, and northern USVI. High Risk of Rip Currents
are in effect for all other beaches, except southern and
southwestern Puerto Rico. For more information and details please
refer to the latest Surf Zone Forecast (SRFSJU), and the Coastal
Hazard Message product (CFWSJU).