National Weather Service San Juan PR
348 AM AST Fri Aug 3 2018
.SYNOPSIS...Lingering moisture from a weak tropical wave will
increased showers today across the local forecast area. A second
stronger tropical wave will move through the area on Monday
enhanced by an upper level trough. A new episode of Saharan dust
will arrive on Saturday and intensify over the weekend. The dust
will last at least through mid week.
&&
.SHORT TERM...Today through Sunday...
Moisture associated with the passage of a weak tropical wave to
south of the region will increase across the area for today with
precipitable water values around 1.7 inches. However, due to the
lack of upper-level dynamics, widespread rainfall activity is not
expected with most of the rainfall activity being limited across
western PR due to local and diurnal effects. Given the recent heavy
rainfall during the past couple of days across western PR, the
terrain is saturated, therefore, the potential will exist for urban
flooding as well as rapid rises along rivers and streams in areas
that do receive heavy rainfall activity. Mudslides in areas of steep
terrain are also possible. Isolated showers in the form of streamers
will be possible downwind from the USVI, affecting Culebra and
eastern PR.
On Saturday, an extensive area of Saharan dust will begin to work
its way across the region. Therefore, hazier skies are expected.
This Saharan dust plume, however, will be not strong enough to
inhibit convection with locally and diurnally induced convection
expected across western and northwestern PR during afternoon.
Additional showers in the form of streamers may develop downwind
from the USVI as well as downwind from El Yunque, affecting southern
portions of the San Juan Metro area.
A more active day is expected for Sunday as a mid to upper-level
trough will be positioned in a favorable location north of the
region to result in the development of more widespread shower
activity. Latest forecast soundings show very unstable conditions
developing with lifted index values around -10 along with very cold
500 mb temperatures between -9 and -10 degrees Celsius. Therefore,
the potential will exist for the development of strong
thunderstorms, especially across the western half of PR, where the
activity will be enhanced by sea breeze convergence and
topographical effects.
.LONG TERM...A tropical wave is forecast to move across the local
region on Monday with upper level dynamics favorable for the
development of widespread showers and thunderstorms across the
local forecast area. Although conditions are expected to be
slightly more stable from Tuesday through Friday, there will be
enough available moisture to generate showers and thunderstorms
mainly over the interior and western portions of Puerto Rico each
afternoon.
&&
.AVIATION...Mainly VFR conditions expected across all terminals
through 03/16z. SHRA and isolated TS expected to develop across
western PR after 03/16z, with TJBQ and TJMZ observing VCTS from
03/18z to 03/22z. This could create MVFR conditions at times,
especially across the vicinity of TJBQ, where the heaviest activity
is expected. Winds will be from the east between 10 and 20KTS with
higher gusts and sea breeze variations after 03/14z.
&&
.MARINE... Winds will continue at 15 to 20 kts and seas mainly of
5 feet or less but occasionally up to 6 feet overnight through
Friday. Small craft operators should therefore continue to
exercise caution.
&&
.FIRE WEATHER...The latest observations and forecast guidance
suggest that there is an elevated risk for fire weather today
across the South Coastal Plains of Puerto Rico. A Fire Weather
Discussion (RFDSJU) has been issued for the South Coastal Plains
of Puerto Rico. There is a low risk of fire weather elsewhere in
Puerto Rico and the U.S. Virgin Islands.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 88 79 89 79 / 20 40 40 30
STT 91 80 90 80 / 30 40 40 30