National Weather Service San Juan PR
503 AM AST Sat Jul 27 2019
.SYNOPSIS...Hazy skies due to Saharan dust and diurnally induced
afternoon showers over western PR are expected during the weekend.
A tropical wave will increase showers and thunderstorms on Monday
and Tuesday. Another tropical wave will move on Wednesday. Hazy
skies due to saharan dust return on Thursday and another tropical
wave moves on Friday.
&&
.SHORT TERM...Today through Monday...
A drier than normal air mass along with suspended Saharan dust will
prevail today through Sunday. This will result in mainly fair
weather conditions along with hazy skies. However, there will still
be patches of low-level moisture embedded within the easterly trade
wind flow moving across the area. Therefore, some passing showers
can be expected across the regional waters and portions of northern
and eastern Puerto Rico and the USVI during the overnight and early
morning hours. This will be followed by the development of showers
and thunderstorms across western portions of Puerto Rico during the
afternoon hours as the shallow low-level moisture combines with
strong daytime heating and sea breeze convergence. At this point,
given the drier than normal air mass along with the suspended
Saharan dust in place, not expecting the activity across western
Puerto Rico to be too significant.
The weather pattern begins to change by Monday as the moisture
content associated with an active tropical wave, currently near 50W
longitude, gradually increases. Latest model guidance has trended a
little slower with the arrival of the tropical wave that now the low
to mid-level moisture content does not begin to increase
significantly until later Monday afternoon and evening. As a result,
scattered showers and isolated thunderstorms are expected to
gradually increase in coverage across the regional waters and affect
portions of the eastern half of Puerto Rico and the USVI during this
time frame. Additional showers and thunderstorms are expected across
western Puerto Rico during the afternoon hours as a result of
strong daytime heating and local effects.
.LONG TERM...Tuesday through Saturday...
Abundant moisture behind the tropical wave with precipitable
water content ranging from 2.00-2.40 inches across the region
will linger on Tuesday. Southeast steering wind flow will keep
showers and isolated thunderstorms streaming from the Caribbean
waters into the U.S. Virgin Islands and east/southeast sections
of Puerto Rio. Additional thunderstorms are forecast to develop
across much of PR through the day. Another tropical wave streams
quickly on Wednesday and in combination with an upper level trough
will maintain an active weather pattern across the islands. A
drier air mass with Saharan dust moves on Thursday, promoting
hazy skies and fair weather conditions. Then on Friday a weak
tropical wave moves quickly across the region, increasing shower
activity once again but not as heavy as earlier in the week. By
Saturday, breezy conditions and another drier air mass with
Saharan dust are expected.
&&
.AVIATION...Mainly VFR conditions expected to prevail through the
forecast period. Hazy skies due to saharan dust will continue,
however, visibilities should remain P6SM. SHRA/TSRA expected across
west and southwest PR between 27/16z and 27/22z, affecting mainly
TJMZ terminal. Brief MVFR conditions cannot be ruled out. Winds will
be out of the ENE at less than 10 kts through 27/13z, increasing to
between 15 and 20 kts with higher gusts and sea breeze variations
after 27/14z.
&&
.MARINE...As winds gradually decrease and range between 10-15 kt
through the weekend, seas are forecast to remain under 5 ft. Hazy
skies will limit somewhat the visibility today. A moderate risk of
rip currents is expected to continue along the northern and
southern beaches of PR and St. Croix.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 79 89 78 / 20 20 20 30
STT 91 80 89 79 / 20 20 10 30