National Weather Service San Juan PR
520 AM AST Wed Jan 3 2024
.SYNOPSIS...Ongoing hazard risks revolve around the possibility of
life-threatening rip current conditions across Atlantic beaches.
The weather pattern should remain fair and stable due to a
persistent mid-level ridging. However, patches of shallow moisture
will generate rain, especially across windward areas at nighttime.
A gradual increase in the available moisture is likely from
Thursday onward, potentially contributing to increased shower
activity. Temperatures will range from below-seasonal to seasonal
levels in the next few days. Nevertheless, above-seasonal
temperatures are likely during the weekend.
&&
.SHORT TERM...Today through Friday...
Fair weather conditions with no shower activity observed across the
islands during the overnight hours. Light land breezes dominated and
minimum temperatures ranged between the low to mid 70s across most
lower elevations of the islands, with at least 1 station at lower
elevations of north-central Puerto Rico reporting a low of 69F.
Minimum temperatures were, as reported by stations, in the low to
mid 60s across higher elevations of Puerto Rico. Localized lower
minimums are likely.
Satellite derived precipitable water (PWAT) values indicate
relatively dry air across the islands, with PWAT at below normal to
normal values for this time of the year. Some patches of shallow
moisture will filter in today and then increase in frequency on
Thursday. Current model guidance indicate relatively dry air again
on Friday with patches of shallow moisture arriving at times. PWAT
should peak at normal values with these patches. The proximity of a
pre-frontal trough to our northwest will help promote winds to
diminish and become generally easterly today. Although winds should
remain generally easterly to ESE through the rest of the period,
they're forecast to veer later become more ENE to end the short term
period. However sea breeze and land breeze variations will be
present.A series of frontal lows and surface high pressures will
continue moving into and across the Atlantic north of the region,
relaxing and tightening the pressure gradient. A mid- to upper-
level ridge will continue to promote drier air aloft and warmer mid-
level temperatures, limiting shower activity.
Brief passing showers carried by shallow moisture can still affect
windward sectors of the islands this morning, but overall weather
conditions will be fair. Patchy fog over areas of the interior
likely this morning. Increased cloud cover and limited convective
activity is also possible over areas of interior to western Puerto
Rico during the afternoon due to local effects. As the frequency of
patches of moisture increases this evening, and tomorrow under more
ESE winds, rain chances will also increase. ESE winds tomorrow will
also promote slightly warmer temperatures across the region.
.LONG TERM...Saturday through Wednesday...
Similar to previous model guidance, changes in the timing of both
peak and diminished moisture levels and alterations in wind
patterns were introduced, given the nature of the expected patchy
weather pattern. While precipitable water (PWAT) variations are
likely, PWAT will remain within seasonal to above-seasonal
moisture thresholds, ranging from 1.2 to 1.7 inches. This new
guidance has delayed the highest and lowest PWAT to Wednesday and
Wednesday night, respectively. Despite these variations, mid-level
ridging and associated strong trade wind cap inversion will hold
across the Caribbean region. However, a slight weakening of the
inversion is likely as polar troughs sink southward across the
western Atlantic and steer the ridge well over the western
Caribbean, allowing moisture to extend beyond the 800 mbar layer.
The general wind flow at lower levels should remain around 5-15
mph from the east throughout the period, with a southeast
component during the weekend and a northeast component on Tuesday
and Wednesday, when wind speeds will likely increase to 10-20 mph,
yielded by a surface high pressure moving eastward across the
western into the central Atlantic.
The anticipated weather pattern will be characterized by passing
showers moving over areas spanning east-northeastern Puerto Rico
and the U.S. Virgin Islands. These showers will be more prevalent
at nighttime and during the wettest and breeziest periods,
especially on Tuesday and Wednesday. Limited afternoon shower
activity is possible across the interior to western Puerto Rico
during the wettest periods. Temperatures should range from the
mid-80s in lower elevations to the mid-50s in higher elevations,
but an increase of 2-5 degrees is possible on Saturday and
Sunday. Overall, the hazards throughout the long-term forecast
period should remain at the lowest risk levels.
&&
.AVIATION...
(06 TAFS) VFR conditions across the terminals. Mainly E to ENE
winds up to 15 knots with sea breeze variations higher gusts
through 03/22Z. Becoming light and variable, dominated by land
breezes after 03/22Z. Some VCSH possible across TJSJ/TIST/TISX,
increasing in frequency after 03/18Z.
&&
.MARINE...
A low pressure system along with its front, moving eastward across
the Western Atlantic, will approach the region and will linger
north of the forecast area today. At the same time, a migrating
high pressure will position over the Central Atlantic through the
end of the workweek. Therefore, expect light to moderate easterly
winds through much of the workweek. Another north swell will reach
the local waters by the end of the week.