National Weather Service San Juan PR
512 AM AST Tue Jun 18 2019
.SYNOPSIS...A surface high pressure across the west-central
Atlantic will slowly move east into the central Atlantic by
tonight, which will keep an easterly wind flow across the local
islands. Mid level high pressure and upper level ridge will
maintain a stable weather pattern today and Wednesday. A tropical
wave will pass just south of the local islands on Thursday,
increasing moisture, while an upper trough axis gets very close to
the local islands. Dry air to follow starting on Friday. Haze due
to Saharan dust expected for the next several days.
&&
.SHORT TERM...Today through Thursday...
A benign weather pattern is forecast to prevail through
Wednesday, as a result of, a relatively drier air mass and Saharan
dust. The combination of the drier air mass and dust will limit
shower development during the afternoon across many areas.
However, moisture embedded in the easterly trades combined with
local and diurnal effects could induce an isolated to scattered
showers through Wednesday mainly across western areas of Puerto
Rico. If showers do develop, they will be short-lived as a result
of a drier air mass and the lack of upper-level forcing.
Additionally, the GFS shows a strong inversion from 700 to 200 mb
this inversion will inhibit the vertical development of showers that
may form during the afternoon. Therefore, rainfall amounts are
expected to be light through Wednesday.
Thursday, a tropical wave is forecast to move across the southern
Caribbean waters, and increase low-level moisture across the area.
The increase in moisture and instability provided by the passing
wave will increase rain changes across Puerto Rico and the U.S.
Virgin Islands.
.LONG TERM...Friday through Wednesday...
After the tropical wave expected on Thursday, the latest guidance
suggests that the local area will dry up significantly and the
available moisture will be below normal for the weekend. So
mostly fair weather is expected during the long term forecast
period. There is an upper trough expected to the northeast of the
local islands on Friday, but it will be too far and the axis will
be to our east, so no impact is expected locally. Thereafter, the
mid and upper levels will remain stable until Tuesday when an
upper trough could dig into the western Caribbean. At this time,
the upper trough appears to be a bit too far west and the dry air
and possible Saharan dust may be too much for any significant
shower and thunderstorm development to occur across the local
area. So essentially, generally fair weather with perhaps
scattered showers expected in the long term.
&&
.AVIATION...VFR conds will continue to prevail across all terminal
sites through 19/03Z. ISO/SCT SHRA are possible by 18/18Z mainly
across the western areas of Puerto Rico. Sfc winds out of the east
at 15 to 20 kts with higher gusts possible. Suspended Saharan dust
particulates will continue to affect the local flying area for the
through Wednesday.
&&
.MARINE...Choppy seas and moderate winds are expected across the
local waters. Seas up to 6 feet and winds up to 20 knots are
expected today and most of Wednesday. The latest guidance
indicates a slight increase in winds across the Caribbean waters
starting on Wednesday night, causing the local seas to slightly
increase through Thursday, causing hazardous seas which would meet
small craft advisory criteria. For today and tonight, there is a
moderate risk of rip currents for most of the beaches in PR except
for western PR. For the USVI, St Croix has a moderate risk of rip
currents across most of the beaches except the western beaches,
then Saint Thomas and Saint John has a low risk.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 78 / 10 20 40 40
STT 89 80 89 80 / 20 20 30 30