Puerto Rico Weather

Area Forecast Discussion

National Weather Service San Juan PR

503 AM AST Mon May 22 2017



.SYNOPSIS...Fair weather conditions will prevail most of the week.

Pulses of Saharan Dust will reach the Northeast Caribbean over the

next several days reducing somewhat the visibilities. A wetter

pattern is possible during the weekend and early next week as an

induced trough and a tropical wave moves across the region.



&&



.SHORT TERM...Today through Wednesday...



Doppler radar indicated isolated shower activity mostly along the

northern sections of Puerto Rico as well as across the

surrounding waters overnight and early this morning. The induced

surface trough northeast of the region will continue to drift

northeastward and away from the region today as a surface high

develops north of the local islands. A weak easterly wave over the

central Caribbean will continue to move westward and also away

from the local area today. Model guidance suggests that Saharan

Air Layer is expected to increase considerably over the Region

today through midweek. This will maintain hazy skies and warmer

than normal temperatures across the region for the next several

days. GFS guidance indicated PWAT values at near 1.60 inches

today, decreasing below 1.50 inches Tuesday and thereafter as a

relatively dry and hazy air mass encompass the region from the

east. However, residual moisture will combine with strong daytime

heating, sea breeze convergence and mountains lifting to induce a

new round of showers and thunderstorms over central interior,

western and northwest Puerto Rico each afternoon. Not significant

precipitation is expected to affect the U.S. Virgin Islands.



.LONG TERM...Thursday through Tuesday...



Upper level ridge will dominate the Northeast Caribbean Thursday

and Friday while an upper level trough amplifies east of the

Lesser Antilles. At the surface...high pressure over the Central

Atlantic will continue to push Saharan Dust particles over the

local area. Therefore...conditions will remain hazy, dry and

relatively stable through the end of the work week. Then...an

induced surface trough will promote moisture convergence and

thunderstorm activity during the weekend. A tropical wave will

follow the surface trough keeping the conditions somewhat unstable

through at least early next week.



&&



.AVIATION...Mostly VFR conditions expected across the local flying

area for the next 24 hours. VCSH/VCTS is possible across TJMZ and

TJBQ after 22/17Z as afternoon convection develops over western and

northwest PR. Winds will increase at 10-15 knots after 22/13Z with

sea breeze variations. Latest TJSJ sounding indicated an easterly

wind flow up to 15 knots from the SFC to 6K feet, becoming light and

variable between 6k-30k feet and then westerly and stronger above

30k feet.



&&



.MARINE...High pressure will build over the Central Atlantic by

midweek resulting in seas building to 5-7 feet across the Atlantic

Waters. Marine conditions will gradually improve through the weekend

when seas will subside to 2-4 feet across most of the waters.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 90 78 91 78 / 30 20 20 20

STT 88 80 89 80 / 20 20 20 20

Area Forecast Discussion

National Weather Service San Juan PR

410 AM AST Wed May 24 2017



.SYNOPSIS...Mostly fair and relatively dry weather conditions

with high concentrations of saharan dust particulates will

continue through the end of the week. An upper level ridge is

forecast to hold over the region until at least Friday. Surface

high across the central Atlantic will maintain an easterly trade

wind flow across the region for most of the forecast period. A

wetter pattern is possible early next week as a tropical wave

moves across the local islands.



&&



.SHORT TERM...Today through Friday...

Partly cloudy skies prevailed across Puerto Rico and the U.S. Virgin

Islands overnight. No shower activity was observed over land areas.

A very dry airmass will continue to dominate the local region for

the next few days as an upper level ridge continues in total control

of the local weather. Saharan dust will continue across the region

today. As a result, hazy skies can be expected. A southeast wind

flow will promote higher than normal temperatures along the northern

slopes of Puerto Rico this afternoon.



Model guidance suggests that Saharan Air Layer is expected to

continue affecting the local region through at least Friday. This

will maintain hazy skies and warmer than normal temperatures across

the region for the next several days. However, by Friday an increase

in moisture is expected. Therefore, an increase in shower activity

is then expected as this moisture, combined with strong daytime

heating, sea breeze convergence and mountains lifting will induce

showers and possible thunderstorms development over central

interior, western and northwest Puerto Rico Friday afternoon.

Significant precipitation is not expected to affect the U.S. Virgin

Islands.



.LONG TERM...Saturday through Thursday...

An upper level low and an associated trough is forecast to develop

just to the east northeast of the region during the upcoming

weekend. This feature is expected to erode the mid to upper level

ridge that persisted over the region for the last few days.

However, the upper trough axis is forecast to remain east of the

region, maintaining the islands on the subsidence side of the

trough. Surface high pressure across the central Atlantic is

expected to maintain moderate easterly trade winds across the

region until early next week. Optical Thickness model guidance

suggests that the Saharan Air Layer will persist over the

region through most of the work week and into the upcoming

weekend, resulting in hazy and a relatively dry airmass across the

local islands. Latest surface analysis depicted a tropical wave

across the tropical Atlantic. This wave will continue to move

westward and approach to the Lesser Antilles late Monday and

Tuesday. It is then forecast to move over the eastern Caribbean

and over the local islands Tuesday through Wednesday. This feature

should bring an increase in tropical moisture transport and

consequently increase the chance for showers and thunderstorms

over the local islands and surrounding waters next week.



&&



.AVIATION...VFR conditions will prevail across all TAF sites through

at least 24/16z. VCSH can be expected across TJMZ and TJBQ with

mountain obscurations. Low level winds will be mainly southeast at

10 to 15 kts with higher gusts.



&&



.MARINE...High pressure building north of the region will aid in

slightly increasing the trade winds across the surrounding waters,

resulting in posible seas building up to 6 feet across the Atlantic

waters and local passages through Wednesday. Marine conditions will

then gradually improve through the weekend when seas subsiding to

4 feet or less across most of the waters.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 91 80 91 79 / 10 10 10 10

STT 89 80 88 79 / 10 10 10 10

Area Forecast Discussion

National Weather Service San Juan PR

500 AM AST Fri May 26 2017



.SYNOPSIS...An upper level trough is forecast to move over the

area by early next week. A tropical wave is forecast to enter and

move across the eastern Caribbean by Tuesday.



&&



Short Term... Friday through Sunday...



The Saharan dust that has been affecting the local area is expected

to clear off today but then increase slightly on Saturday into

Sunday. However, the concentrations do not seem to be as high as it

has been this past week. The available moisture is expected to also

increase today with precipitable water values at around 1.5 inches

and hanging on close to that value thorough the weekend. The local

winds will remain from the east at about 10-15 mph due to the strong

surface high pressure across the central Atlantic. There is an upper

low to the northeast of the local islands that is expected to move

west a little bit then north and east as it weakens and dissipates

by Sunday. This means that the upper level dynamics do not seem to

be particularly conducive to sustained thunderstorm development even

with less Saharan Dust concentrations. For that reason, the forecast

is for isolated to scattered showers with afternoon convection

occurring across western PR every afternoon this weekend.



Long Term...Monday through Saturday...



Latest model guidance indicated an upper level trough is forecast

to move over the area by early next week. Also, a tropical wave

is forecast to enter and move across the eastern Caribbean by

Tuesday. These two features promise to bring an increase in low

level moisture across the region beginning on Monday night and

continuing through most of next week. As a result, showers and

thunderstorms are expected to affect the region.



&&



.AVIATION...VFR conds expected through the forecast period. Winds

from the east with sea breeze variations at about 10-15kt and

occasional gusts. VCSH likely for TJMZ and TJBQ after 26/16Z due to

afternoon convection across western PR. SHRA activity to dissipate

mostly over PR by 26/23Z.



&&



.MARINE...Seas up to 6 feet and winds up to 20 knots can be

expected across the local waters. Small Craft should exercise

caution across the Atlantic water north of Puerto Rico. Moderate

risk of rip currents expected today across much of the beaches of

the islands.







&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 89 78 90 77 / 10 40 40 20

STT 88 78 88 77 / 20 40 40 30

Area Forecast Discussion

National Weather Service San Juan PR

437 AM AST Sun May 28 2017



.SYNOPSIS...A mid to upper level trough will continue to linger and

deepen across the northeastern Caribbean, while a Tutt low is forecast

to develop just north of the forecast area late Monday through Tuesday.

A tropical wave just east of the Lesser Antilles will enter the eastern

Caribbean early Monday then move across and impact the local area through

at least Tuesday.



&&



.SHORT TERM...Sunday through Tuesday...



Partly cloudy skies prevailed across the local islands overnight and

early this morning with a few passing showers noted across the surrounding

waters, USVI and E PR. These showers however left minimal rainfall accumulations.

The overnight temperatures were in the upper 70s to low 80s across the

lower elevations and in the low 70s across the higher elevations. Winds

were east northeast at 10 mph or less.



A developing mid to upper level trough across the west tropical Atlantic

and into the central and eastern Caribbean will enhance shower and

thunder activity across the eastern Caribbean through the forecast

period. At lower levels, a tropical wave will continue to move way

from the forecast area today, however another wave and associated

moisture is expected to reach the local islands as soon as Monday

afternoon/night. This feature will combine with the developing mid

to upper level trough to result in organized convection across the

area Monday afternoon and Tuesday. Meanwhile, at least through Monday

morning, continue to expect passing showers across windward areas

during the morning and evening hours as well as showers and thunderstorms

developing over and west of the Cordillera Central in the afternoon.

With the heaviest shower and thunder activity, urban flooding will

be likely.



.LONG TERM...Wednesday through Monday...



The tropical wave with axis near 55W is forecast to move across and

exit the eastern Caribbean by Wednesday. However, expect sufficient

trailing moisture along with the lingering mid to upper level Tutt low

to maintain instability and good moisture convergence across the region.

This will support a fairly moist weather pattern and consequently favorable

conditions for showers and isolated thunderstorm development across

the islands and over the coastal waters at least until Thursday, with

a gradual improvement by Friday and Saturday. Still however will not

rule out the potential for early morning passing showers and isolated

thunderstorm development each day over portions of the islands,especially

over the central and west sections of Puerto Rico. In addition, recent

dust prediction models and guidance suggests another moderate to high

concentration of Saharan dust trailing the previously mentioned wave.

Therefore, will have to see how much this would affect the overall

environment. Present model guidance also suggest another tropical

wave is to approach the region by Sunday and Monday, which is typical

for this time of the season when tropical waves are likely every two

to three days. Will continue to monitor and adjust forecast package

as needed.



&&



.AVIATION...Mostly VFR conds expected at all TAF sites through the

morning hours with VCSH possible at the Leeward and USVI terminals

as well as JSJ. Aft 28/16z SHRA/TSRA expected over PR and this may

result in brief periods of MVFR conds at all PR TAF sites. Easterly

winds 10-15 knots with some sea breeze variations after 28/12z.

Approaching tropical wave may result in SHRA/TSRA over the Leeward

terminals later today.



&&



.MARINE...Overall buoys across the regional waters continued to

suggest seas between 2-4 feet and winds east to northeast at 10 to

15 knots. Seas are expected to remain between 2 to 5 feet through

early next week and winds of 15 knots or less in most areas.

However, a tropical wave forecast to move across the eastern

Caribbean may bring an increase in winds and seas as well as

increase the chance for thunderstorm activity Monday through

Tuesday.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 89 78 89 77 / 40 30 50 50

STT 89 78 86 77 / 40 40 60 60

Area Forecast Discussion

National Weather Service San Juan PR

450 AM AST Tue May 30 2017



.SYNOPSIS...A trough aloft will continue to interact with

moisture associated with a departing tropical wave to result

in periods of showers and thunderstorms today. The proximity

of this trough will continue to enhance afternoon showers and

thunderstorms Wed-Thu. A more seasonable weather pattern is

expected Fri-Sat with the next tropical wave passage on Sunday.



&&



.SHORT TERM...Today through Thursday...



Abundant amounts of moisture trailing the tropical wave and the

instability aloft due to the lingering mid to upper level

trough/TUTT, continued to favor the development of showers and

isolated thunderstorms across the region during the overnight and

early morning hours. Expect these unstable conditions to continue

today, but with a slight break in cloudiness, shower and

thunderstorm activity by mid morning.



However, instability aloft and good moisture convergence along with

daytime heating will quickly give way to another round of afternoon

convection across the islands especially over the interior and west

sections of Puerto Rico. Showers and or isolated thunderstorms may

also form along the Yunque area then stream across the San Juan

metro area during the afternoon.



Expect the tropical wave to exit the region later today however

recent models guidance continued to suggest a TUTT low will

continue to develop and linger just north of the region through

Thursday. Although this feature will shift slowly eastward during

the period, Upper level divergence/diffluence associated with this

feature should persist over the northeastern Caribbean. This will

therefore maintain unstable conditions which in combination with

ample trade wind moisture transport and local effects, will

continue to enhance the development of showers/thunderstorms

across the regional waters and parts of the islands each day at

least through Thursday. The activity on Wednesday and Thursday

should however be less widespread as lesser moisture pooling is

expected due to somewhat drier air filtering from the east along

with a fine to moderate concentration of Saharan dust.



.LONG TERM...FRIDAY THROUGH WEDNESDAY...



The aforementioned mid to upper level trough/TUTT low...which is

now located north of Hispaniola...will move eastward while

weakening with its associated axis crossing the local islands on

Friday. As this feature weakens Sat-Sun, a weak mid level ridge

pattern is expected to slowly build across Caribbean. At lower

levels, a tropical wave will reach the eastern Caribbean on

Sunday, bringing once again plenty of tropical moisture to the

forecast area. After the wave passage, a broad surface high

pressure across the central Atlantic will promote east southeast

winds Monday through much of the next work week.



Therefore, if the long term forecast holds, expect a seasonal

weather pattern Friday and Saturday with locally induced showers

and thunderstorms, followed by a wetter period on Sunday and early

Monday associated with a wave passage. Fair weather conditions

with warm to hot temperatures are expected next work week under

a mid level ridge pattern and east southeast winds.



&&



.AVIATION...SHRA/ISOLD TSRA across the local flying til at least 30/12z.

This will result brief MVFR en route btw islands with VCSH or SHRA

at TJSJ/TJNR/TNCM/TKPK. Aft 30/16z...SHRA/ISOLD TSRA psbl at and

vcty TJMZ/TJBQ. Also, psbl MVFR at TJSJ due to isold streamer-

like SHRA/TSRA from el Yunque area. Latest TJSJ sounding indicated

ESE winds below FL050 at 10-22 kts. Sfc wnds lgt/vrb bcmg E-NE

10-15 kts at most terminals except for local sea breeze

variations.



&&



.MARINE...Moisture associated with a departing tropical wave will

continue to result in periods of showers and thunderstorms today.

Seas are expected to remain at or below 6 feet and winds at 15-20

knots, particularly across the Caribbean waters. Mariners are

advice to exercise caution as winds and seas could be locally

higher in the vicinity of thunderstorms. There is a moderate risk

of rip currents across most of the local beaches.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 87 79 86 79 / 40 20 40 40

STT 89 80 87 80 / 40 50 50 40

Area Forecast Discussion...DELAYED

National Weather Service San Juan PR

520 AM AST Thu Jun 1 2017



.SYNOPSIS...A mid to upper level trough will continue to prevail

across the forecast area through at least Friday, weakening during

the upcoming weekend. The next tropical wave passage is expected on

Sunday. A dry and stable air mass will prevail across the forecast

area the next week.



&&



.SHORT TERM...Thursday through Saturday...



Today, June 1st 2017, Atlantic Hurricane Season begins. 2017

Hurricane Season runs from June 1st to November 30th. During the

Hurricane Season, make a well-informed decision "BE PREPARED".



Showers slowly diminished across the local islands overnight.

Shower activity should continue to decrease in intensity and

coverage through the morning hours, as a drier air mass makes its

ways from the east into the local islands. Although a mid to upper

level trough is over the region, this dry slot is forecast to

limit afternoon convection over PR to the western sections of the

island. So the eastern half of the island as well as the USVI

should have only isolated to scattered showers.



A surge of moisture is expected to reach the islands tonight into

Friday, increasing the coverage and intensity of showers and

thunderstorms. By Saturday, the islands will be in the convergence

area of the left entrance of the mid-upper level trough. This will

limit the potential for showers and thunderstorms on Saturday.



.LONG TERM...SUNDAY THROUGH FRIDAY...



As a tropical wave moves across the eastern Caribbean but mainly

south of the area on Sunday; precipitable water is expected to

increase with values near or above the normal range which is 1.75

inches. However, moisture is expected to quickly erode as soon as

late Monday as a mid to upper level ridge builds across the forecast

area and hold much of the next week. At lower levels, a surface high

pressure across the central Atlantic will yield an east southeast

wind flow Sunday through at least Thursday.



As a result, if the forecast holds, the best chance for shower and

thunder activity is Sunday and Monday with passing showers across

the USVI and E PR during the morning hours followed by showers and

thunderstorms developing across west sections of Puerto Rico in the

afternoon. A fair weather pattern with warm to hot temperatures and

hazy skies is expected Tuesday and onwards.



&&



.AVIATION...VFR conds expected across the local terminals with VCSH

possible at USVI terminals as well as TJSJ and TJBQ. SHRA/TSRA

possible after 01/17Z across western PR which could affect TJMZ.

Winds will be mainly from the east at 5-10KT increasing aft 01/13z

at 10-15 kt with gusts up to 25 kts and sea breeze variations

along the coastal sections.



&&



.MARINE...Seas 3 to 5 feet and winds 15-20 knots are expected to

prevail across most of the local waters...except seas near 6 feet

over the Atlantic waters later today. Small boat operators should

exercise caution. There is moderate risk of rip currents across

most of the local beaches, increasing to high tomorrow night

across the north facing beaches of Puerto Rico.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 85 78 87 78 / 30 40 40 20

STT 90 79 86 79 / 30 30 30 20

Area Forecast Discussion

National Weather Service San Juan PR

511 AM AST Sun Jun 4 2017



.SYNOPSIS...

A mid to upper level ridge will build from the west over the

region through the first part of the upcoming week. An upper

level trof will amplify from the east over the North East

Caribbean around midweek. A tropical wave will continue westward

across the Caribbean Sea. A broad surface high pressure over the

Atlantic ocean will continue to induce an east to southeast wind

flow.



&&



.SHORT TERM...Today through Wednesday...Clear to partly cloudy skies

prevailed across Puerto Rico and the U.S. Virgin Islands overnight.

Dry weather conditions prevailed most of the night with no shower

activity observed over land areas. However, early this morning, a

line of showers moved quickly across the eastern half of Puerto

Rico. For today, lingering moisture will combine with daytime

heating and local effect to produce scattered showers with isolated

thunderstorms over the western interior and northwest sections of

Puerto Rico this afternoon. Rest of the area will enjoy mostly sunny

skies with little shower activity.



For Monday into Wednesday, a very dry airmass is forecast to

encompass the region. As a result, limited shower activity is

expected, with only some light passing showers affecting the local

islands from time to time, mainly during the early morning hours.



.LONG TERM...

Although a mid to upper level ridge is forecast to persist across

the islands, a trof aloft is expected to amplify near the region

from the east by the second half of this week. GFS and ECMWF

disagree in the final position and the strength of this trof

aloft. In addition, a second tropical wave is forecast to enters

the Caribbean Sea around mid week, moving near the islands

Thursday or Friday.



&&



.AVIATION...

VFR conditions can be expected across most TAF sites

through 04/16Z. Brief periods of MVFR conditions with mountain

obscuration are possible across TJBQ and TJMZ this afternoon. Low

level winds will be mainly southeast at 10 to 15 kts except for sea

breeze variations across coastal areas.



&&



.MARINE...

A northerly swell continue moving across the Atlantic and

Caribbean Passages. Mariners can expect seas between 4 and 6 feet

across these waters, and should exercise caution. Elsewhere, seas

at 5 feet or less are expected with easterly winds at 10 to 15

knots.



There is a high risk of rip currents from the northwest coast of

Puerto Rico to the north central coastline. Refer to the Surf

Zone Forecast (SRFSJU) for additional information. Along the other

beaches in Puerto Rico and the U.S. Virgin Islands can expect a

low to moderate risk of rip currents.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 92 79 91 79 / 20 10 10 10

STT 89 81 88 80 / 20 20 20 10