Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 041359
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
959 AM AST Thu Jun 4 2020

.UPDATE...

Mostly sunny skies are prevailing across the region this morning
with easterly winds up to 15 mph. Current temperature at Luis
Munoz Marin International Airport is 88 degrees; with the mid to
upper 80s observed over the metro areas of San Juan. The record
high temperature for the airport is 93 degrees, there is a chance
that we tie or break this record this afternoon. Elsewhere,
daytime high temperatures of the upper 80s to the lower 90s are
expected. A drier air mass and a mid-level ridge are providing the
fair weather conditions across the region. Later today, locally
and diurnally induced showers and isolated thunderstorms are
forecast to develop over portions of western Puerto Rico.

&&

.AVIATION...

Mainly VRF conditions to prevail across the local areas. SCT
SHRA/TSRA are possible across western and northern PR by 04/17,
this could cause VCTS near terminals TJMZ and TJBQ until 05/02Z.
Winds out of the east at 10 to 20 kts with higher gusts and sea
breeze variations after 04/14Z.

&&

.MARINE...

Moderate to fresh winds from the east to east-southeast
today will result in choppy seas. The winds are expected to be up
to 20 knots with occasional higher gusts, and wave heights up to 6
feet today and on Friday. Therefore, small craft operators are
urged to exercise caution.

&&

.PREV DISCUSSION... /issued 411 AM AST Thu Jun 4 2020/

SYNOPSIS...Drier than normal moisture and moderate easterly
winds will cause mainly fair weather across the local islands for
the next few days. However, some locally induced convection across
western Puerto Rico will remain possible in the afternoons.
Slightly above normal temperatures are also be expected, with
highs in the upper 80s to low 90s across the lower elevations. The
marine conditions will also be choppy for the rest of the
workweek. A change in weather pattern is expected next week,
although with considerable uncertainty, it appears that the
chances of rain will increase next week.

SHORT TERM...Today through Saturday...

Generally fair weather conditions expected to prevail across most of
the local area through the short term period as the combination of a
drier than normal air mass and a mid-level ridge will serve to limit
the shower activity. Having said this, there will still sufficient
moisture in the lower-levels to combine with local and diurnal
effects to generate scattered showers and isolated thunderstorms
across portions of western Puerto Rico each afternoon. However,
significant rainfall activity is not expected. Some brief trade wind
showers cannot be ruled out at times during the overnight and early
morning hours across portions of eastern Puerto Rico and the USVI.
Breezy conditions are also expected through the period as a broad
surface high pressure settles across the central Atlantic, helping
to tighten the local pressure gradient.

LONG TERM...Sunday through Friday...

The weather pattern appears to change for this next week, although
there is considerable uncertainty and the model guidance has been
somewhat inconsistent with its timing and intensity, there is
consistency in the fact that some change is coming to the local
weather pattern. This change will probably mean a few days with
an increased chance of showers and thunderstorms. First of all the
local winds are expected to diminish significantly due to a
surface trough to the north of the local area, causing a COL
starting on Monday and persisting through at least Wednesday.
Although the wind direction is expected to remain mainly from the
SE, the wind speeds will diminish to 10 mph or less, in many cases
inland staying around 5 mph. There will be an increase in
moisture with precipitable water values being near to above
normal. There will also be an upper trough that will be
strengthening and will close into an upper low by the end of next
week. This upper trough will help cause instability across the
local area and provide support for thunderstorm development. That
said, the different global models differ in the timing for when we
will have the best support for thunderstorms. The GFS model being
the wetter model, especially for eastern PR, where the GFS put a
bullseye of heavy precip on Monday afternoon. Given all this
information it is worth mentioning again that uncertainty is high
in the long term forecast, especially for timing and intensity of
possible rain and thunderstorms, but it appears likely that a
change in pattern will be observed next week.

AVIATION...Mainly VFR conditions to prevail across the local area. Sct
SHRA/TSRA possible across western and northwestern PR between 04/17
and 04/22z, resulting in VCTS across TJMZ/TJBQ terminals. Winds
expected to be mainly from the E at less than 10 kts through 04/12z,
increasing to 15 to 20 kts with higher gusts and sea breeze
variations after 04/14z.

MARINE...Moderate to fresh winds from the east to east-southeast
today will result in choppy seas. The winds are expected to be up
to 20 knots with occasional higher gusts, and wave heights up to 6
feet today and on Friday. Therefore, small craft operators are
urged to exercise caution. Winds and seas are expected to improve
starting this weekend; by the following workweek, the winds are
expected to be gentle and the wave heights generally between 2-3
feet.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  90  80  90  78 /  10  20  20  30
STT  90  80  89  78 /  10  20  20  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...TW
LONG TERM....JA
PUBLIC DESK...LIS


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