Re: Caribbean - Central America Weather
Posted: Thu Aug 19, 2021 5:21 am
Area Forecast Discussion
National Weather Service San Juan PR
446 AM AST Thu Aug 19 2021
.SYNOPSIS...Mainly fair weather conditions will prevail across
the area throughout the day today. A tropical wave will move
across the Caribbean waters later today into Friday. Drier
conditions along with hazy skies due to a Saharan Air Layer is
expected later on Friday through Saturday. Another tropical wave
will move across the area on Sunday, followed by another period of
mainly fair weather conditions during the early to middle portion
of next week as a drier than normal air mass with another Saharan
Air Layer moves across.
&&
.SHORT TERM...Today through Saturday...
A weak upper level high pressure to the northwest of the local
islands will continue to weaken and move southwest and away from the
local area. Meanwhile, an upper level low over the Bahamas, and
another one in the western central Atlantic will gradually move
south as they strengthen. By Saturday afternoon, the Tropical
Upper Tropospheric Trough (TUTT) in the Atlantic would have
strengthen considerably and positioned itself to the north of the
local islands. Based on the latest guidance, there will be
convection related to this TUTT on Saturday, but it will be to the
south of the local islands. So basically a rather benign weather
pattern, with somewhat limited shower activity is expected in the
short term forecast period.
Another thing to note is that there will be Saharan dust over the
local area starting late today and continuing into Friday and
Saturday. This means that hazy skies will persist now through the
end of the week. Therefore there will be only a slight chance of
showers in the overnight and the morning hours. During the
afternoon, sea breeze convergence and diurnal heating will promote
shower development across the western areas of Puerto Rico. A
tropical wave will pass to our south late tonight into Friday. The
abundance of Saharan dust expected, and the inversion seen in the
forecast soundings, may cause the rainfall amounts this afternoon
and Friday to be modest.
Daytime high temperatures across will be near the upper 80s to lower
90s in the lower elevations and the upper 70s to mid 80s in higher
elevations during the short-term period.
.LONG TERM...Sunday through Thursday...
A tropical wave is expected to move across the area on Sunday and
will interact with the TUTT, which will be situated north of the
area. The combination of these features could result in an
unstable conditions with an increase in shower and thunderstorm
activity across portions of the local area. Thereafter, a fair
weather pattern is expected during the early through middle
portion of next week as a drier than normal air mass carrying with
it Suspended Saharan Dust particulates moves over the area. This
will increase the trade wind inversion and thus will limit shower
activity. Nevertheless, some afternoon convection will still be
possible across portions of western Puerto Rico due to local
effects and diurnal effects. Another tropical wave may affect the
area by the end of the long term period.
&&
.AVIATION...VFR conds expected across the local terminals through
the forecast period. Winds will be light early in the morning, but
will increase to around 15KT gusting to 25KT after 19/14Z from the
ENE with sea breeze variations at TJPS. Saharan dust is expected
after around 19/20Z, causing HZ, but VIS is expected to remain P6SM.
However, we are monitoring the possibility of VIS to be affected
with higher concentrations of Saharan Dust after the current 24 hr
forecast period.
&&
.FIRE WEATHER...A drier than normal air mass is expected to
prevail across the local area through this afternoon and with
winds expected to be from the east-northeast, relative humidity
values are forecast to drop into the middle 40s for a couple of
hours during the late morning into the afternoon hours. Winds are
also expected to peak at around 15 mph with frequent higher gusts.
KBDI values across the Camp Santiago area remain above 600, which
is above the critical threshold level. Therefore, the combination
of all of these factors will support an elevated fire danger
threat, mainly across the southeastern coastal plains, for today.
&&
.MARINE...Seas of 5 feet or less with moderate to fresh easterly
winds of between 15 and 20 knots will prevail across the local
waters for today. A tropical wave will move across the Caribbean
waters later today into Friday, increasing the winds and shower
activity. Choppy seas are expected Friday and Saturday. Another
tropical wave along with a wind surge are expected Sunday into
Monday, and seas could become hazardous with small craft
advisories possible.
For beachgoers, a moderate risk of rip currents is expected across
the northern and some of the southern beaches of Puerto Rico, the
eastern beaches of Vieques and Culebra, some of the southern
beaches of Saint Thomas and Saint John, and most of the beaches of
Saint Croix.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 78 / 20 30 20 20
STT 91 80 88 80 / 30 30 10 10
National Weather Service San Juan PR
446 AM AST Thu Aug 19 2021
.SYNOPSIS...Mainly fair weather conditions will prevail across
the area throughout the day today. A tropical wave will move
across the Caribbean waters later today into Friday. Drier
conditions along with hazy skies due to a Saharan Air Layer is
expected later on Friday through Saturday. Another tropical wave
will move across the area on Sunday, followed by another period of
mainly fair weather conditions during the early to middle portion
of next week as a drier than normal air mass with another Saharan
Air Layer moves across.
&&
.SHORT TERM...Today through Saturday...
A weak upper level high pressure to the northwest of the local
islands will continue to weaken and move southwest and away from the
local area. Meanwhile, an upper level low over the Bahamas, and
another one in the western central Atlantic will gradually move
south as they strengthen. By Saturday afternoon, the Tropical
Upper Tropospheric Trough (TUTT) in the Atlantic would have
strengthen considerably and positioned itself to the north of the
local islands. Based on the latest guidance, there will be
convection related to this TUTT on Saturday, but it will be to the
south of the local islands. So basically a rather benign weather
pattern, with somewhat limited shower activity is expected in the
short term forecast period.
Another thing to note is that there will be Saharan dust over the
local area starting late today and continuing into Friday and
Saturday. This means that hazy skies will persist now through the
end of the week. Therefore there will be only a slight chance of
showers in the overnight and the morning hours. During the
afternoon, sea breeze convergence and diurnal heating will promote
shower development across the western areas of Puerto Rico. A
tropical wave will pass to our south late tonight into Friday. The
abundance of Saharan dust expected, and the inversion seen in the
forecast soundings, may cause the rainfall amounts this afternoon
and Friday to be modest.
Daytime high temperatures across will be near the upper 80s to lower
90s in the lower elevations and the upper 70s to mid 80s in higher
elevations during the short-term period.
.LONG TERM...Sunday through Thursday...
A tropical wave is expected to move across the area on Sunday and
will interact with the TUTT, which will be situated north of the
area. The combination of these features could result in an
unstable conditions with an increase in shower and thunderstorm
activity across portions of the local area. Thereafter, a fair
weather pattern is expected during the early through middle
portion of next week as a drier than normal air mass carrying with
it Suspended Saharan Dust particulates moves over the area. This
will increase the trade wind inversion and thus will limit shower
activity. Nevertheless, some afternoon convection will still be
possible across portions of western Puerto Rico due to local
effects and diurnal effects. Another tropical wave may affect the
area by the end of the long term period.
&&
.AVIATION...VFR conds expected across the local terminals through
the forecast period. Winds will be light early in the morning, but
will increase to around 15KT gusting to 25KT after 19/14Z from the
ENE with sea breeze variations at TJPS. Saharan dust is expected
after around 19/20Z, causing HZ, but VIS is expected to remain P6SM.
However, we are monitoring the possibility of VIS to be affected
with higher concentrations of Saharan Dust after the current 24 hr
forecast period.
&&
.FIRE WEATHER...A drier than normal air mass is expected to
prevail across the local area through this afternoon and with
winds expected to be from the east-northeast, relative humidity
values are forecast to drop into the middle 40s for a couple of
hours during the late morning into the afternoon hours. Winds are
also expected to peak at around 15 mph with frequent higher gusts.
KBDI values across the Camp Santiago area remain above 600, which
is above the critical threshold level. Therefore, the combination
of all of these factors will support an elevated fire danger
threat, mainly across the southeastern coastal plains, for today.
&&
.MARINE...Seas of 5 feet or less with moderate to fresh easterly
winds of between 15 and 20 knots will prevail across the local
waters for today. A tropical wave will move across the Caribbean
waters later today into Friday, increasing the winds and shower
activity. Choppy seas are expected Friday and Saturday. Another
tropical wave along with a wind surge are expected Sunday into
Monday, and seas could become hazardous with small craft
advisories possible.
For beachgoers, a moderate risk of rip currents is expected across
the northern and some of the southern beaches of Puerto Rico, the
eastern beaches of Vieques and Culebra, some of the southern
beaches of Saint Thomas and Saint John, and most of the beaches of
Saint Croix.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 78 / 20 30 20 20
STT 91 80 88 80 / 30 30 10 10