National Weather Service San Juan PR
437 AM AST Mon Nov 4 2019
.SYNOPSIS...
A deep trough continues to affect the area, bringing above average
shower activity to the region, which could lead to urban and small
stream flooding, as well as a risk of localized flash flooding. A
drier air mass will begin to filter in over the area tomorrow.
This will bring somewhat calmer conditions, though afternoon
convection is still anticipated. Renewed moisture is expected for
this weekend, with the potential for a weak tropical wave. Rough
marine conditions will also continue to be a concern in the local
waters into the latter half of the week.
&&
.SHORT TERM...Today through Wednesday...
A mid to upper level trough with its associated low will linger to
the east northeast of the local islands through today, then
weakening and slowly lifting northwards by late Tuesday. There is
also a SFC trough to the east of the local area which is slowly
moving west and will increase moisture today through Tuesday. This
weather pattern will cause good instability across the local area.
Showers and isolated thunderstorms could be observed in the morning
and nighttime hours, but in the afternoon the diurnal heating will
play a role and cause the development of significant showers and
scattered thunderstorms across the interior into western PR, with
less frequent showers elsewhere in PR. Given the amount of rainfall
observed yesterday and all of the urban and small stream flooding
that was observed, it is expected for additional urban and small
stream flooding to occur over PR today, while rapid river rises and
localized flash flooding will not be ruled out this afternoon over
PR especially in the interior and western sections. The instability
decreases for Tuesday and Wednesday, but scattered showers are still
expected overnight and in the morning hours, while afternoon
convection is forecast across western PR. The USVI has a good chance
of rain today, in fact, the expected shower activity could cause
minor ponding of water on poor drainage areas. Since the instability
decreases after today, mainly brief and isolated to scattered
showers are expected for the USVI.
.LONG TERM...Thursday through Monday...
Thursday into Friday, a trend towards slightly increased moisture is
expected, with patches of moisture embedded in the trade winds
making their way into the area. Sufficient moisture is expected to
be in place over the area such that showers, with the potential
for isolated thunderstorms are anticipated in the afternoons,
especially in western and interior Puerto Rico. During the
overnight and morning hours each day, passing showers are possible
over local waters, the USVI, and eastern coasts of Puerto Rico,
as well as the north coast on Thursday night, with a shift in the
winds bringing the flow to out of the northeast.
Continuing increases in the moisture level locally are expected for
the weekend. The GFS has backed off on its predictions for the
amount of moisture compared to yesterday. Even so, increasing
moisture will aid in the development of showers and possible
isolated thunderstorms over the local islands in the afternoons,
especially over western and interior Puerto Rico. Acting to limit
the convective activity is a TUTT, forecast to stretch southwest,
bringing its tail to east of the area on Saturday, putting us on
the subsidence side of the system. On Sunday, the TUTT retreats to
the northeast, decreasing the impedance to convection caused by
the upper level convergence. This will likely lead to an increase
in thunderstorm activity compared to the previous day. There is
also the potential for streamers to form both days downwind of
orographic features such as the major islands east of mainland
Puerto Rico and El Yunque; with winds generally out of the
southeast, potential impacts could include the San Juan metro
area.
Drier air is expected to filter into the region on Monday, which is
anticipated to bring a decrease in activity in the afternoons.
However, there will remain enough moisture over the area to allow
for the development of afternoon showers and isolated thunderstorms
due to local effects and daytime heating.
&&
.AVIATION...
SHRA is expected in the morning hours across the local
flying area, causing at least VCSH across TJSJ, TIST, and TISX.
TEMPO SHRA possible at TJSJ causing a brief reduction in visibility.
After 04/16Z, VCSH will remain a possibility for all of the local
terminals, but TSRA is expected across western PR, which will affect
the vicinity of TJPS, TJBQ, and TJMZ. TSRA is likely at TJMZ after
04/18Z which will cause MVFR conds and TEMPO IFR until around
04/21Z. Winds will be mainly from the east at around 10KT with sea
breeze variations developing after 04/13Z.
&&
.MARINE...
Seas up to 6 feet are anticipated across much of the local waters,
including the majority of the local Atlantic waters; small craft
operators should exercise caution. The swell from last week has
largely subsided, but a wind surge is forecast to bring another
increase in wave heights by mid-week. Conditions are likely to
meet small craft advisory criteria for offshore waters and
passages. A high risk of rip current persists today for northern
beaches of Puerto Rico, with a moderate to high risk along the
beaches of Culebra, as well as northern and eastern beaches of St.
Croix.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 86 76 88 75 / 50 50 30 30
STT 87 76 87 77 / 50 50 20 20