Heat Advisory 2, NWS JSJ

Area Forecast Discussion
National Weather Service San Juan PR
117 PM AST Mon Sep 30 2019

.SYNOPSIS...

There remains lingering moisture over the islands this afternoon,
aiding in the development of showers and isolated thunderstorms due
to local effects and daytime heating, especially in northern
portions of Puerto Rico. Increasingly dry conditions are anticipated
tomorrow through Thursday. Late on Friday, a weak tropical wave is
forecast to push into the forecast area, followed by a somewhat
stronger one on Sunday and another likely arriving on Tuesday next
week.

&&

.SHORT TERM...Today through Wednesday...

Showers and isolated thunderstorms are expected for this afternoon,
largely in northern and northwestern Puerto Rico in a generally
southerly wind flow, caused by local effects and daytime heating.
Some of these showers have already begun to develop, most notably
in north central portions of the island. Drying conditions will
be seen tomorrow through Thursday. That being said, there is
likely to be sufficient moisture in lower levels to fuel the
development of afternoon convective activity. With the mean flow
being out of the south/southeast over the next few days, the area
with the highest potential for showers and isolated thunderstorms
associated with this activity will remain to be northern and
northeastern Puerto Rico. The drier air aloft is forecast to
somewhat suppress this activity and rainfall amounts will be
generally lower compared to that of the previous days.

Warmer than average temperatures are possible, especially in
northern coastal areas, as warmer air from the south influences the
islands. The drier conditions will also likely serve to increase
daytime heating. Heat indices in the low 100s are possible.

.LONG TERM...Thursday through Tuesday... From Prev Discussion...

Southeast flow on Thursday at lower levels will bring drier air at
first, then a weak easterly wave with a patch of moisture will come
through on Friday. On Saturday moisture increases again, until the
next and more significant tropical wave moves through the area on
Sunday. Drying on Monday will be followed by even better moisture on
Tuesday with another tropical wave. At upper levels, low pressure
will move west into the Caribbean while higher pressure is draped
across the western Atlantic just north of Puerto Rico. The high and
the low will both move west and away from the area Friday and
Saturday leaving northeast flow over the area. That flow will
continue through Tuesday as a strong TUTT low approaches the
Caribbean on Sunday but weakens before moving across on Tuesday.
Models show enhanced divergence on Sunday afternoon with the passage
of the first significant tropical wave.

At this time the driest period looks to be Wednesday and Thursday,
while Saturday and Sunday and possibly the Tuesday after next will
have the best moisture for shower and thunderstorm activity. Mid
level temperatures will also decrease a degree or two Sunday through
Tuesday to add some extra instability.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across
all terminals during the next 24 hours. However, SHRA/TSRA may
cause tempo MVFR conds thru 22z at TJBQ/TJSJ. Low level winds will
continue from the south between 10-15 kts, bcmg light and
variable overnight at the sfc.

&&

.MARINE...

Seas continue to subside in the Atlantic waters this afternoon, as
the effects of swells off of Hurricane Lorenzo diminish. For the
rest of today and tomorrow, seas up to around 6-6.5 feet are
possible, with further decreases expected during the second half of
the week. Elsewhere, relatively tranquil marine conditions will
continue through the week; wave heights in the Caribbean waters will
be up to around 3-6 feet.

Rip current will remain a concern on local beaches. There is a low
to moderate risk this afternoon in the U.S. Virgin Islands as well
as Vieques and Culebra. Southeastern Puerto Rico has a moderate risk
of rip currents, while north-facing beaches will have a moderate to
high risk.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  78  93  78  92 /  10  20  10  20
STT  81  88  80  88 /  10  10  10  10

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk from Tuesday morning through Tuesday
     afternoon for Northeast-Southeast.

     High Rip Current Risk from 6 PM AST this evening through Tuesday
     afternoon for North Central-San Juan and Vicinity.

     High Rip Current Risk through Tuesday afternoon for Northwest.

VI...None.
AM...None.
&&

SHORT TERM...DS
LONG TERM....CRS

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