National Weather Service San Juan PR
453 AM AST Sun Nov 19 2023
.SYNOPSIS...
Expect dry and stable conditions to prevail across the islands
today. This pattern should continue through at least Monday when
better moisture approaches from the west, which may increase
rainfall the following days. Hazardous marine conditions will
continue due to a strong north- northeasterly swell and moderate
to locally fresh south wind. Seas and breaking waves are reaching
around 10 feet due to this, therefore exercise caution when
spending time around the ocean.
&&
.SHORT TERM...Today through Tuesday...
Conditions will remain dry and stable over most of the region today
as most of the remnants from the large plume of moisture associated
with the former tropical disturbance are now expected to stay to the
west of the region and over the Dominican Republic. However mid to
upper level cloud debris will continue to spill across the region
steered by the upper level west to southwest wind flow. Southerly
low level winds will persist across the region with the continued
intrusion of drier air from the south and east along with suspended
dust particulates steered by south to southeast low level winds.
Good mid to upper level compression and the presence of Saharan dust
particulates trapped in the low levels will promote warmer than
normal conditions which will persist overnight, and consequently all
official stations at San Juan, and USVI airports have reported the
warmest minimum temperatures on record for yesterday.
Presently,The Doppler Radar and satellite imagery showed the
aforementioned line of showers and thunderstorms west of Puerto
Rico,lingering over the Dominican Republic and Mona passages and being
steered by the prevailing southerly low level wind flow. Recent
guidance now suggest that this plume will be slowly lifted mainly
northwards between the Dominican Republic and the Mona passage
overnight through Sunday, with only fragmented moisture expected to
eventually reach portions of western Puerto Rico later today.
For the rest of the day and into Monday, overall dry conditions will
prevail across the most of the islands as model guidance suggests
that the mid to upper leve ridge and continued intrusion of Saharan
dust particulates, will maintain the area on the dry and subsident
side of the upper trough which is forecast to quickly move north of
the region today through Monday. A southerly low level wind flow
will persist through Monday, then by late Monday though Tuesday
winds, are to shift and become more northerly as a high pressure
ridge will build across the southwest Atlantic. This in turn will
bring return remnant moisture from the north and west, associated
with the aforementioned moisture plume as well as that from a
frontal shearline that will sink southwards across the area. As a
result, increasing low level moisture is forecast by Monday
afternoon into Tuesday with this time frame now expected to be the
best potential for shower and isolated thunderstorm development
across the islands and coastal waters. At this time widespread
rainfall is now anticipated, however there will be increased chance
for excessive rainfall in isolated areas and thus potential for
urban and small stream flooding along with ponding of water on roads
and poor drainage areas especially on Tuesday. Stay tuned!
&&
.LONG TERM...Wednesday through Sunday...
No significant changes were introduced to the long-term forecast.
The latest model guidance suggests Wednesday as a transition day
from a wet/unstable pattern to gradual drying and stable weather
conditions. By mid-week, expect the wind flow to gradually turn
northeasterly due to the proximity of a dissipating frontal
boundary to the north of the forecast area. On Thursday, the
surface high-pressure system over the western Atlantic will
position across the central Atlantic, promoting east-to-southeast
winds through the weekend. As mentioned, a gradual decline in
available moisture is expected after Wednesday, with precipitable
water values dropping below seasonal normal thresholds (below 1.5
inches) as additional patches of dry air filter across Puerto Rico
and the U.S. Virgin Islands. The decrease in precipitable water
levels should lower the likelihood of precipitation and diminish
the risk of flooding by Friday into the weekend.
In general, during this period, expect mostly calm and stable
weather conditions across the islands. However, occasional trade
wind showers in the morning across eastern Puerto Rico and the
U.S. Virgin Islands and the typical afternoon convection across
western PR due to diurnal heating and sea breeze variations cannot
be ruled out.
&&
.AVIATION...VFR conditions will persist through the prd. Hazy
skies will persist due to suspended Saharan dust particulates
across the region, but no restriction to flight VIS is
anticipated. A line of showers may impact The Mona passage between
western PR and the Dominican Republic with SHRA/Isold TSRA psbl
btw 19/06-10z. SFC wnd mainly fm S at 10 kt or less, increasing
between 10-20 kts aft 19/14z. Isold SHRA/TSRA may develop ovr
regional waters of the ATL and coastal waters west of Puerto Rico
durg aftn.
&&
.MARINE...Latest buoys from the CARICOOS network shows seas
ranging around 4-7 feet across the local waters and passages as
a north-northeast swell continues to make its way into the our
forecast area with periods around 12 and 14 sec. Hazardous marine
conditions remain across the Atlantic Ocean and Caribbean
Passages.Therefore, Small Craft Advisories continue in effect for most
local waters.