621
FXCA62 TJSJ 292015
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
415 PM AST Sun Sep 29 2024

.SYNOPSIS...

A gentle northeast flow has set up over the local area.
Good moisture and above normal temperatures will produce scattered
showers and isolated thunderstorms over the local waters overnight
and early morning and over western and interior Puerto Rico from
late morning to late afternoon each day through Friday.

&&

.SHORT TERM...Tonight through Tuesday...

Showers and thunderstorms began a little before noon and were spread
from Saint John to Yauco. Then just after noon thunderstorms began
from Lares to Anasco and Rincon. So far radar is reporting maximum
amounts up to 2 inches, but no flooding had been reported as of 3 PM
AST. Temperatures were just a little cooler across the area, but
heat indices did reach 120 in Vega Baja and 116 in Cotton Valley.
Heat indices reached 108 plus in many of the advisories areas. The
high so far in San Juan was 91 degrees.

At the surface a high pressure system is located over the western
Atlantic, north of the Bahamas, and will maintain light winds from
the northeast to east today. A drying trend will continue today
through Tuesday morning across the region with precipitable water
values falling to around 1.7 inches. However, the available moisture
in combination with daytime heating and local effects will result in
the development of strong showers and thunderstorms in the afternoon
hours again Monday and Tuesday. There is also the potential to
observe showers across the San Juan metropolitan area and adjacent
municipalities with the streamer formation. During the overnight
hours showers with isolated thunderstorms are possible over the
local waters. For the USVI, a few showers will develop over the
local waters and the upstream showers could move over the islands
with minor accumulations.

The TUTT low moving southwest into the Caribbean Sea has crossed the
Leeward Islands and set up an intense gradient over Puerto Rico
between it and an upper level high east of Florida. This will move
west into the Dominican Republic tonight. It has been responsible
for the activity over western Puerto Rico.

Warm to hot conditions are likely to continue this week with an
elevated to significant heat threat. Highs will continue to soar
into the upper 80s to mid 90s along the coastal and urban sectors of
Puerto Rico and the U.S. Virgin Islands. Residents and visitors
should take precautions to stay hydrated by drinking plenty of
water, wearing light and breathable clothing, and avoiding prolonged
exposure to the sun, especially during peak heat hours.

Although the Atlantic Basin will likely see Tropical Cyclones Kirk,
Leslie and Milton develop in the next 10 days, at this time none are
expected to reach Puerto Rico or the U.S. Virgin Islands.

&&

.LONG TERM...Wednesday through Sunday...
//from previous discussion//

A drying trend is expected to continue on Wednesday as the
layered ridge over the western Atlantic sinks further into the
north-central Caribbean. Winds at the surface will remain NNE
through at least Saturday as the region remains under the
influence of the ridge to our west/northwest and a tropical
cyclone over the far Tropical Atlantic. However, a surge in low-
level moisture from the Atlantic waters is expected to move over
the area by Thu-Fri, while an upper level trough over the western
Atlantic continues to move into the northeastern Caribbean during
the weekend. Therefore, showers and thunderstorms will increase in
coverage and intensity once again later in the forecast period,
but should develop mainly over the interior and southern sections
of the islands during the afternoons. For the USVI, shower activity
will increase mainly on Thursday and Friday.

&&

.AVIATION...
(18Z TAFS)

VFR conds will prevail thru 30/15Z except over land under SCT
SHRA/TSRA til 29/22Z, where mtn obscurations and MVFR CIGS and
MVFR/IFR vsbys will exist. SHRA are moving 260/12 KT which is also
the general flow for now. Some land and sea breeze influences will
be seen at the sfc. Maximum winds NE 72-82 kt btwn FL390-450. Sea
breezes will return at 30/14Z.

&&

.MARINE...

A high pressure system over the western Atlantic will maintain
light to gentle northeast to easterly winds. Seas will remain around
3 to 5 feet over the next few days. Showers remain possible across
the waters. Thunderstorms will diminish later in the week.

&&

.BEACH FORECAST...

There is a moderate risk of rip current for western, northern,
and eastern PR, Culebra, Saint Thomas, and Saint Croix.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for Prz005-002-
005-008.

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

$$

SHORT TERM/AVIATION...WS
LONG TERM...GRS
PUBLIC DESK...ICP/MMC