National Weather Service San Juan PR
501 AM AST Sat May 21 2022
.SYNOPSIS...
The Saharan Air Layer will continue to produce hazy skies
throughout the day. Warmer temperatures and heat indices in the
low 100s are also possible each day, especially for north-central
Puerto Rico and urban areas of the islands. A surface high
pressure over the Atlantic Ocean will promote an easterly wind
flow across Puerto Rico and the U.S. Virgin Islands. A TUTT will
slowly erode the ridge aloft, increasing instability early next
week.
&&
.SHORT TERM...Today through Monday...
Surface high pressure over the western Atlantic will maintain an
easterly flow across the Northeast Caribbean. Embedded in the trade
winds are the Saharan dust particles that will continue to spread
across the local islands today. However, higher concentrations will
remain just south of Puerto Rico and St. Croix, over the Caribbean
Sea. Aerosols models suggest that the dust will diminish on Sunday.
Therefore, visibilities will gradually improve over the next 24-36
hours. In terms of moisture and stability, dry and stable conditions
associated with a mid-level ridge will prevail most of the day
across most of the forecast area. However, sea breeze combined with
available moisture produce some showers over the western interior of
Puerto Rico, but those showers will be short-lived under the
influence of the mid-level ridge. Elsewhere, hazy skies with little
or no shower activity are expected.
An upper-level trough/TUTT will erode the high pressure at mid-
levels allowing more moisture andinstability to pull over the area
Sunday into early next week. Fragments of moisture over the western
Atlantic will be pulled over the local area tomorrow, enhancing the
trade wind showers during the morning hours on Sunday. Then, a
subtropical jet will provide better dynamic aloft to sustain longer
the showers over western Puerto Rico on Monday afternoon.
.LONG TERM...Tuesday through Saturday...
A lingering TUTT-low will promote a long wave trough pattern from
the central Atlantic into the northeastern Caribbean through much
of the long-term period. A surface low pressure over the Central
Atlantic will relax the local pressure gradient, weakening the
local winds. A surface high pressure moving from North America
into the Western Atlantic will tight the local pressure gradient
increasing the winds after Wednesday onward.
A seasonal weather pattern will dominate the local weather
conditions next week. The seasonal weather pattern consists of
passing showers with periods of moderate to locally heavy rains
overnight and early in the morning across the Virgin Islands and
eastern Puerto Rico. This activity will be followed by afternoon
convection across the interior and western sections during the
afternoon, where isolated thunderstorms could develop each day.
Urban and small stream flooding will remain possible with the
heaviest activity.
&&
.AVIATION...
VFR conditions will prevail thru the forecast period. Easterly
winds will continue at 15-20 kt with higher gusts. Hazy skies
associated with Saharan dust particles will keep the visibilities
across the flying area between 6-8 SM.
&&
.MARINE...
Seas will remain at 5 feet or less across the local waters and
passages. A surface high pressure over the central Atlantic will
maintain gentle to moderate east to southeast winds across the
local waters and passages, and local effects will increase local
winds each day. A small northerly swell is forecast to arrive
across the local Atlantic waters today.
Beachgoers, a high rip current risk is expected for the beaches
of the north central Puerto Rico.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 76 89 77 / 10 20 30 50
STT 86 77 86 76 / 10 20 20 50