Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/06/23

Area Forecast Discussion

National Weather Service San Juan PR

 904 PM AST Mon Jun 5 2023

.UPDATE...The latest upper air sounding indicated 1.46 inches of
precipitable water, and stable conditions aloft with plenty of
low to mid-level dry air. This is due to a Saharan Air Layer that
is producing hazy skies in general across PR and the USVI. Overall
dry conditions will continue tonight and on Tuesday morning with
little to no precipitation across the forecast area. Another hot
day is expected on Tuesday, with heat indices possibly exceeding 112
degrees Fahrenheit along the coastal and urban areas of the northern
coast of PR and Culebra. Therefore, an Excessive Heat Watch (NPWSJU)
remains in effect through at least Tuesday afternoon.


&&

.AVIATION...Mainly VFR conditions are expected across all
terminals during the next 24 hours. HZ due to Saharan dust
expected through the period. No change from prev discussion. The
06/00z TJSJ sounding indicated south winds up to 18 kt blo FL050.


&&

.MARINE...Relative tranquil seas will continue through Tuesday.
Latest coastal buoy readings indicates seas at less than 4 feet
and winds up to 10 knots.


&&

.PREV DISCUSSION... /issued 409 PM AST Mon Jun 5 2023/

SYNOPSIS...

Expect a gradual drying pattern for the next few days. Hazy skies
due to Saharan dust is also expected, with the highest concentrations
by mid-week. Rainfall activity will be limited at least through
the first half of the workweek. Tranquil marine conditions will
continue through the week.

SHORT TERM...Tonight through Wednesday...

Relatively stable conditions prevailed across Puerto Rico and the
U.S. Virgin Islands today. It is worth mentioning that hazy skies
somehow dominated the forecast area. This pattern is associated
with the dry air with Saharan dust particles that filtered into
the region with the southerly flow. Once again, temperatures in
the coastal areas fluctuated in the 90s and the mountains in the
mid to upper 80s. The maximum temperature at the Luis Munoz Marin
International Airport was 94F. As anticipated, the heat indices
in areas where the Excessive Heat Warning was in effect fluctuated
from 103 to 114 degrees Fahrenheit and slightly higher in
localized areas, while in sections where the Heat Advisory was in
effect, the heat index exceeded 100 degrees. A weather observer
from Hatillo, Puerto Rico, reported 120 degrees Fahrenheit at 2:11
PM AST in his station. The U.S. Virgin Islands also experience
heat indices near to slightly above 100 degrees. In St. Croix, the
index reached 103 degrees. Undoubtedly, another hot day here in
the tropics.

At this time, the deep layer high-pressure system over the eastern
Atlantic and the deep layer trough are promoting breezy southerly
winds over the tropical islands. The Excessive Heat Warning and
the Heat Advisory for the lower elevations remain in effect until
5 PM AST. Not to be left out that the Excessive Heat Watch will
continue until Tuesday afternoon.

The latest model guidance suggests a dominating drier pattern
during the short-term period, especially mid-week. This pattern
will prevail as the dry air mass keeps filtering into the islands
lowering the precipitable water content to below-normal values for
this time of the year. Therefore, Fire Weather conditions will be
possible during the driest days. As mentioned in the previous
short-term discussion, any available moisture will remain in the
lower levels as a ridge, and the dry air continues to dominate the
mid to upper levels. The probability of precipitation for this
forecast period remains low.

LONG TERM...Thursday through Tuesday...FROM previous
discussion...

Stable weather conditions are expected to prevail during the
long- term forecast period. A high pressure system at all levels
will continue to hold just northeast of the islands. This feature
will drive the winds from the southeast through Saturday. Breezy
conditions will persist throughout this period, with a low level
steering flow of 15-20 knots. A Saharan Air Layer will remain in
place too, with hazy skies expected. So far, the aerosol models
have the highest concentration lingering into early Friday. Due to
dry air aloft, shower activity will be limited during this
period. On Friday, fragmented patches of moisture associated with
old frontal boundaries will be push into the islands from the
circulation of the high pressure. Moisture content will increase,
and so will the probability of showers, with passing activity
expected to reach the eastern coast of Puerto Rico and the U.S.
Virgin Islands. This activity is not expected to be significant.

For the weekend, another pulse of dry air and Saharan particulate
will approach the islands. The surface high will weaken a little,
allowing for the trade winds to resume from the east. However, this
will not last long, as the winds will veer to the southeast by
early next week. During this period, any rainfall activity will be
associated with small patches of moisture approaching the area.
However, the climatological outlook from the Climate Prediction
Center does favor below than normal precipitation for this period,
and since June is typically a dry month, little rainfall
accumulation is anticipated.

In terms of temperatures, 925 mb temperatures will drop a little by
Friday, and again on Monday and Tuesday. This may allow for just a
very small relief from the very high heat indices experienced so
far. Nevertheless, values are expected to remain around advisory or
warning criteria, especially for the urban areas of northern and
northwestern Puerto Rico, and between 102 to 107 for the Virgin
Islands. The users are advised to follow heat prevention guidance
during this prolonged hot forecast period.

AVIATION...VFR conditions are expected across the terminals thru at
least 06/16Z area-wide. SE winds will diminish to less than 12 kt
at most sites and may be calm on some north coasts thru 06/12Z.
Aft 06/14Z low level SE winds up to 10-18 kts will resume--
strongest on the S coast with gusts to 23 kt. Saharan dust will
cont byd 07/02Z, though VSBYS greater than 8 SM are expected
everywhere. Airmen should be sure to check the density altitude
capabilities of their aircraft due to the abnormally hot weather.
Maximum winds S 20-25 kts btwn FL030-060.

MARINE...No changes were introduced into the marine forecast.
Seas remain 4 feet and winds remain out of the south. No
significant events are expected to impact the local waters, and
seas around 2-4 feet will prevail throughout the forecast period.
The risk of rip currents will be low for all the local beaches.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Watch through Tuesday afternoon for PRZ001-005-
     008-012.

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

$$

DSR/ICP