National Weather Service San Juan PR
449 AM AST Sat Jun 11 2022
.SYNOPSIS...A tropical wave moving across the region today could
bring a few roundsof showers and thunderstorms across Puerto
Rico and theU.S. Virgin Islands through tonight. Wetter conditions
will be short-lived as moisture associated with the wave will
move fairly quickly across the region, giving way to drier and
stable conditions as well as the hazy skies through early next
week. Anotherperiod of unsettled conditions isforecast between
Wednesday and Thursday under the influence of an upper trough.
&&
.SHORT TERM...Today through Monday...
At the surface, a high pressure will continue to promote moderate to
fresh easterly winds across the forecast area. Embedded in this wind
pattern, cloudiness and moisture from a tropical wave arriving the
local islands will create more frequent passing showers in the
morning hours. As the day progress, weather conditions should
deteriorate mainly over the interior and western sections of Puerto
Rico. Isolated thunderstorms are included in the forecast, due to
colder temperatures at 500 MB. A significant change in the weather
conditions is forecast for Sunday, when a big pulse of Saharan Air
Layer (SAL) moves into the area and erode most of the present moisture
over the region. This drier conditions will promote very stable
conditions. However, the local effects with the daytime heating
could result in localized shower activity over the interior and
western sections of Puerto Rico. But no significant rainfall accumulations
are expected due to stable conditions aloft. On Monday, the surface
high pressure will move into the central Atlantic resulting in easterly
trade winds that will push fragments of low level moisture over the
area. Nevertheless, the presence of the SAL will limit the shower
coverage across the region. Additionally, stable conditions aloft
will erode the moisture in the mid levels, limiting the vertical
development of the afternoon shower Sunday and Monday.
.LONG TERM...Tuesday through Saturday...
Surface high pressure over the north-central Atlantic will promote
east to east southeast winds across the local area early in the week.
Some Saharan dust particles will still be embedded in the trade
winds on Tuesday but concentrations will be much less than Monday.
GFS forecast soundings suggest precipitable water values slightly
below normal around 1.5 inches on Tuesday afternoon due to the
presence of the Saharan Air Layer at mid-levels. Therefore, expect
a few morning showers on the windward side of the islands followed
by isolated to scattered afternoon convection over the northwest
quadrant of Puerto Rico.
Then, conditions will become wetter and unstable by midweek. An upper-
level trough/TUTT will slowly move westward and position west-northwest
of the region on Wednesday. As the TUTT becomes near stationary north
of Hispanola, deep tropical moisture is forecast to surge from the
eastern Caribbean into the local islands late Wednesday into Thursday.
The high moisture content will combine with enhanced instability associated
with the TUTT to support organized convection in the Caribbean waters
and portions of Puerto Rico and the U.S. Virgin Islands. At this time,
operational modelssuggest that the most active day will be on Thursday
as moisture and instability peak across the local region. However, the
exact timing of the unsettled period may be adjusted early in the week
as operational models still show some discrepancies in the intensity
and the position of the TUTT low. Beside of the uncertainty in
the forecast, there is a decent chance to experience showers and
thunderstorms between Wednesday and Thursday. Afterwards, drier
and more stable conditions are forecast for Friday into next
weekend as the TUTT weakens significantly and mid-level high
pressure expands over the eastern Caribbean. As the ridge spreads
westward into the local region, dry air aloft will limit the
shower coverage as well as the vertical development of the showers
late in the workweek and the weekend. There is a lot of Saharan
dust in the tropical Atlantic between Africa and the Caribbean,
therefore hazy skies will probably accompany the stable conditions
during the weekend.
&&
.AVIATION...Mainly VFR conditions will prevail at all TAF terminals
during the period. VCSH will prevail for TIST,TISX & TJSJ TAF sites
due to the arrival of a tropical wave until 06/18Z. Showers at
10/16Z could add VCTS over TJBQ and more lower ceilings. SFC winds
will increase up to 15 knots and winds gust at 10/14Z to 10/22Z.
Winds will slightly diminish around 10/22Z.
&&
.MARINE...Moderate to locally fresh winds have resulted in choppy
seas of 4-6 feet. Therefore, small craft operators should exercise
caution across most of the local waters. Also, the small northerly
swell has combined with the wind waves to produce a high risk of
rip current for the north coast beaches of Puerto Rico and Culebra
as well as the east coast beaches of St. Croix through at least
Sunday afternoon. For the rest of the local beaches, the risk will
remain moderate except the beaches of Anasco, Mayaguez and Cabo
Rojo where the risk is low.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 89 79 / 50 20 20 20
STT 88 79 89 78 / 50 20 20 20