598
FXCA62 TJSJ 042124
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
524 PM AST Fri Oct 4 2024

.SYNOPSIS...

A high risk of rip currents will be in effect through at least
Sunday at 6 PM on most beaches in northern Puerto Rico, Culebra,
and St. Croix. Long-period swells from Hurricane Kirk will
maintain dangerous coastal conditions throughout the weekend,
particularly Saturday night and Sunday. A Small Craft Advisory is
also in effect through at least Sunday at 6 PM for the offshore
Atlantic Waters. Variable conditions will prevail through the
weekend with afternoon convection mainly affecting interior to
southern PR. Winds will turn with a southerly component early next
week bringing warmer-than-normal temperatures and variable
weather.

&&

.SHORT TERM...Tonight through Sunday...

Afternoon showers and thunderstorms concentrated mainly over
southern PR, under northeast winds. Currently, the highest
rainfall accumulations were over Ponce with, a radar estimated,
1.9 inches observed. This prompted the issuance of a Flood
Advisory for Ponce and Juana Diaz. This convective activity
already weakened and moved offshore. Highs were in the upper 80s
to low 90s across lower elevations of the islands. Heat indices
above 108 degrees were also observed across various lower
elevation areas. Satellite derived precipitable water (PWAT) values
indicate values ranging from 1.90 to 2.00 inches across the
islands. PWAT values of up to 2 inches will continue to filter
into the islands through the weekend, decreasing somewhat on
Sunday.

A mid to upper level trough will approach the northeast Caribbean
from the north-northwest, this will promote a gradual weakening
of the mid to upper ridge during the weekend and increasing
instability The northeasterly wind flow that has affected the
islands during the past workweek will continue tonight due to the
influence of the distant Major Hurricane Kirk and a surface low
across the North Atlantic. This pattern will, however, start
losing ground as an easterly component gradually increases
tomorrow, due to Kirk pulling northward. By Sunday, light
southeasterly flow is forecast. During the short term period,
overnight passing showers will continue across windward sectors.
Minimum temperatures will be in the the upper 70s to low 80s
across coastal sectors of the islands and around the upper 60s to
low 70s across higher elevations of Puerto Rico. Sea breeze
convergence, diurnal heating, and local effects will promote
afternoon showers and isolated thunderstorms, mainly over interior
to southern Puerto Rico, and downwind of the local islands
tomorrow. Light flow can help maintain developing afternoon
convection in the interior on Sunday, drifting afterwards. Heat
indices above 105 degrees will persist across various lower
elevation areas. Afternoon shower and t-storm activity will then
gradually dissipate and/or move offshore each late afternoon to
evening.

.LONG TERM...Monday through Friday...

./FROM PREV DISCUSSION...Issued at 437 AM AST Fri Oct 4 2024/

The latest model guidance suggests that the beginning of the work
week will have a wet pattern with precipitable water values above
the climatological normal. Additionally, the Galvez-Davison Index
indicates a potential for isolated-to-scattered thunderstorm
development over Cordillera Central of PR. Therefore, the
potential for limited to elevated flood risk exists for the
interior, northern, and northwestern of PR, including the San Juan
metro area. Rainfall accumulations on urban areas, roads, small
streams, and washes with isolated flash floods cannot be ruled
out.

The dry pattern is still expected on Tuesday as relative humidities
at mid-levels will plummet below 30 percent. Limited shower activity
can be anticipated. However,  humidity will increase on Wednesday
and remain within the seasonal normal for the rest of the workweek.
This will result in the typical pattern of shower activity across
windward coastal areas during night and morning hours. In the
afternoon, showers and thunderstorms can be expected across interior
and western/northwestern sections of Puerto Rico.

Winds with a southerly component will result in warmer-than-normal
925 mb temperatures. Therefore, limited to elevated heat risk will
prevail for coastal and urban areas of PR and USVI until Thursday.

&&

.AVIATION...

(18Z TAFS)

VFR conds to prevail across the forecast area and at all terminals.
The prevailing light NE SFC winds less than 10 kts will persist
through the period. Brief wnd gust may accompany the passing
showers. SHRA/Isold TSRA psbl along ctrl interior and SRN PR with
VCTS at TJPS TIL 04/23Z. Fm 05/03z-05/14Z additional SHRA/-SHRA will
affect the coastal waters with some reaching the north and east
coastal areas of the USVI terminals and TJSJ. Periods of reduced VIS
and low ceilings are possible with passing SHRA/Isold TSRA with
brief Mtn top obscr psbl ovr E interior of PR w/ passing SHRA. SFC
wnds will incr to btw 10-12kts aft 05/14Z with enhanced sea breeze
variations.

&&

.MARINE...

The interaction of the weak high pressure system over the western
Atlantic and Hurricane Kirk across the Central Atlantic will promote
light to gentle north to northeast winds. Showers with thunderstorm
activity will create locally hazardous marine conditions for small
craft, specially during the afternoon hours near the coastal areas of
PR. A combination of north northeast to northeast long-period swells
will reach the regional waters this evening and continue through the
weekend, generating hazardous seas.

&&

.BEACH FORECAST...

A high risk of rip currents will be in effect this weekend on most
beaches in northern Puerto Rico, Culebra, and St. Croix. Long-
period swells from Hurricane Kirk will maintain dangerous coastal
conditions throughout the weekend, particularly Saturday night and
Sunday. Beachgoers and water sports enthusiasts are urged to use
extreme caution as rip currents can be dangerous along the
northern and eastern coasts of Puerto Rico and adjacent islands.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Sunday afternoon for PRZ001-002-
     005-008-012.

VI...High Rip Current Risk through Sunday afternoon for VIZ002.

AM...Small Craft Advisory until 6 PM AST Sunday for AMZ711.

&&

$$

SHORT TERM....DS
LONG TERM.....MRR
PUBLIC DESK...GRS