Puerto Rico Weather

Area Forecast Discussion

National Weather Service San Juan PR

508 AM AST Sat May 6 2017



.SYNOPSIS...Easterly winds will prevail through the early part of

next week before shifting slightly to the northeast as a surface

high develops to the northwest of the local area. Upper ridge to

prevail through Monday then an upper trough moves over the local

islands on Tuesday through Thursday with an upper jet being

forecast by the long range models. Locally induced showers and

thunderstorms expected this afternoon across the northwestern

quadrant of PR with near normal moisture expected.



&&



.SHORT TERM...Today through Monday...Ridge aloft will persist through

Sunday limiting shower development to the western interior of PR

and streamers forming off the USVI. Steering winds from the

southeast will focus rain activity over sections of NW PR and

streamer type light rain showers could develop from el Yunque area

into the metropolitan area this afternoon. Left isolated

thunderstorms on the forecast as there is a slight chance of short

lived thunderstorms each afternoon. Same pattern expected on Sunday.

Max temps should reach the high 80s and the low 90s across the

coastal areas of southern PR and other urban areas of the island,

across the rest of the islands max temps should range between the

mid to high 80s. Later on Monday the upper ridge weakens as deep

polar trof pattern across the Western Atlantic amplifies into the

local area. This will create favorable upper levels for thunderstorm

development across the Mona Passage and the Atlantic waters.



.LONG TERM...Tuesday through Sunday...

Available moisture is expected to increase quite a bit on Tuesday

into wednesday at the same time that an upper trough with

relatively strong winds, up to 75 knots according to the GFS

forecast soundings, is expected to move into the local area. This

setup, if it were to verify, will bring an increase in shower and

thunderstorm activity over the local area. There also appears to

be a weak moisture boundary to the north of the local area as a

surface high pressure develops to the northwest of the area,

bringing northeasterly winds to the local area.



Thereafter, we move into the subsident side of the upper trough

but still with relatively strong upper level winds. However, late

next week into next weekend we could expect typical convection for

the season which are showers and thunderstorms over PR in areas of

sea breeze convergence with isolated to scattered brief showers

elsewhere in PR and over the USVI.



&&



.AVIATION...Mainly VFR conditions expected to prevail across all

terminals during the next 24 hours. However, VCTS/tempo MVFR conds

possible at TJBQ between 06/18z-22z due to diurnally induced

SHRA/TSRA across the NW quadrant of PR. East to southeast winds at

12-18 kts with higher gusts after 14z due sea breeze variations.





&&



.MARINE...





&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 88 77 88 76 / 20 20 20 20

STT 86 77 87 77 / 20 20 20 20

Area Forecast Discussion

National Weather Service San Juan PR

407 AM AST Mon May 8 2017



.SYNOPSIS...Upper level ridge is forecast to continue to

deteriorate from this afternoon and Tuesday as an upper trough

approaches the local area. A weak surface high pressure over the

central Atlantic will maintain an east to east southeast wind flow

across the northeast Caribbean through early next week.



&&



.SHORT TERM...Today through Wednesday...Variably cloudy skies

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

morning. Passing showers were observed across the eastern half of

Puerto Rico with some affecting the U.S Virgin Islands as well.

Passing showers embedded in the trade winds are expected to continue

through the morning hours. Moisture is expected to increase today as

an approaching deep polar trough and associated frontal system

combined with daytime heating and local effects this afternoon.



For Tuesday and Wednesday, the aformentioned trough, with light

southeast to south wind flow at the surface will promote the

development of showers and thunderstorms across the region. Under

the southeast to south wind flow, better shower activity will be

expected north of the Cordillera Central and across the eastern half

of Puerto Rico.



.LONG TERM...The upper trough axis remain over the northeast

Caribbean, abundant low level moisture will keep favorable

conditions for the development of shower and thunderstorm activity

across the local islands and surrounding waters through at least Thursday.

Guidance suggests that the trough axis will shift to the east of

the region over the Lesser Antilles, late Thursday through

Friday.



The Subsidence area of the upper trough will move over the local

region. This will maintain the region under the stable side of

the upper trough, and therefore limiting the showers and

thunderstorms development over the local islands. The available

moisture will be near normal from late Wednesday until at least

Friday with the return to the typical weather pattern with showers

and thunderstorms during the afternoons due to the combination of

daytime heating and local effects across.





&&



.AVIATION...Passing showers are expected to affect TIST, TIST, and

TJSJ through at least 08/16Z. Periods of MVFR conditions with

mountain obscurations can be expected in the vicinity of TJSJ, TJMZ

and TJBQ from 08/16Z through at least 08/22Z in SHRA/TSRA. Low level

winds will be mainly southeast at 10 to 15 kts.





&&



.MARINE...Winds will slightly increase along the Atlantic near

shore waters up to 20 knots and seas will remain at around 6 feet

across the Atlantic offshore waters, therefore small craft should

exercise cautions across these waters. For the rest of the local

waters, seas are expected to be 5 feet or less for the next

several days with winds at 15 knots or less for the next few days

as well. There is a moderate risk of rip currents for the northern

coast of PR and some beaches in Vieques, Culebra and Saint Croix.







&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 88 75 87 75 / 40 30 50 50

STT 85 75 83 75 / 40 40 50 50

Area Forecast Discussion...UPDATED

National Weather Service San Juan PR

508 AM AST Wed May 10 2017



.SYNOPSIS...

An upper level trough meandering aloft will combine with abundant

low level moisture enhancing showers and thunderstorm activity

through at least late Thursday. A mid to upper level ridge is

expected to build over the region by Saturday into next week. At

the surface, troughs will move across the islands the next few

days. A surface high pressure over the central Atlantic will

maintain an east to east southeast wind flow across the northeast

Caribbean for the next few days.



&&



SHORT TERM...Today through Friday...



The broad band of moisture from an old frontal boundary has moved

into the Leeward islands and will stall there today. This has caused

mid and upper level clouds to clear--at least temporarily--and will

provide additional heating for the activation of shower and

thunderstorms around midday across much of western and interior

Puerto Rico. Southeast flow at the surface will cause showers to

again favor the northwest portion of the island. Although a short

wave has passed through the area and caused good convection,

thunderstorms and some flooding, we are still in the broad base of

the upper level trough that will continue to generate very favorable

conditions today and tomorrow. On Friday upper level support ends

and we are on the back edge of the moisture at mid levels, this will

limit the convection that will be favored by strong heating.



Although showers will continue through the period, the most intense

showers and thunderstorms are expected today and another round of

heavy rain may trigger some river flooding and areas of urban and

small stream flooding which will exasperate the situation of already

saturated and unstable soils to create mudslides. Therefore a flash

flood watch will be issued for the period from noon today to 6 PM

AST today.



.LONG TERM...Saturday trough Wednesday...

A ridge aloft is expected to build over the region by the upcoming

weekend into next week. However, model guidance quickly bring a

tropical wave with abundant tropical moisture across the region

Sunday or Monday. This scenario can increase the potential for

showers and thunderstorms across the islands. Moisture is forecast

to rapidly decrease Tuesday into mid week. The lingering moisture

will result in periods of showers and thunderstorms during the

afternoons and early evening hours due to the combination of

daytime heating and local effects mainly along the Cordillera and

western sections of Puerto Rico. The U.S. Virgin Islands, as well

as the windward sections of PR, can expect passing showers mainly

during the overnight and early morning hours each day.



&&



.AVIATION...

Isold SHRA will continue across eastern PR and

local waters to the north through 10/14Z. Aft 09/16Z afternoon

SHRA/TSRA developing across PR, but mainly wrn and interior, will

cause mtn obscurations and VCSH/VCTS at TJBQ, TJMZ, TJPS, and

possibly TJSJ between 09/17Z and 04/23Z. TEMPO MVFR conds possible

at TJBQ/TJMZ between 09/18Z and 04/21Z. Winds will be mainly from

the ESE at 5-15KT with sea breezes developing after 04/14Z. Max

winds west 50-70 kts at FL410-470 incrg thru 11/12z.



&&



.MARINE...

Mariners can expect seas between 2 and 5 feet across the region,

but are urged to exercise caution across the Anegada Passage and

the U.S. Virgin Islands surrounding waters due to winds between

15 to 20 knots. Elsewhere expect east to east southeast winds

between 10 and 15 knots. Seas expected to continue at less than 5

feet for the next several days. A trof pattern will enhance

showers and thunderstorms formation across the coastal waters.

Therefore, mariners and beach goers should be alert and monitor

the local marine products as weather conditions can deteriorate

quickly over the waters and coastal areas.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 86 76 86 76 / 50 30 30 20

STT 84 76 85 75 / 50 40 40 30



&&

Area Forecast Discussion

National Weather Service San Juan PR

514 AM AST Sun May 14 2017



.SYNOPSIS...A tropical wave will move west across the Caribbean--

mainly south of the area--today and spread better moisture across

Puerto Rico and the U.S. Virgin Islands this afternoon through

Monday. Then southeasterly flow around the western end of high

pressure over the tropical Atlantic will bring somewhat drier air

over the area through most of the week. Showers and thunderstorms

will increase today and Monday, but will still occur each day in

the northwestern two thirds of Puerto Rico.



&&



.SHORT TERM...Early this morning through Tuesday...

Mainly isolated showers are across the local waters, with only a

few expected to brush some of the islands during the morning

hours. This will be followed by mostly sunny skies during the late

morning and early afternoon. However, with the gradually

increasing low level moisture advection along with local and

diurnal effects, expect showers and possibly isolated

thunderstorms to develop once again over parts of the central

interior and northwest sections of PR. Elsewhere mostly sunny

skies are expected, but some areas may experience isolated

showers of short duration mainly downwind of the islands over the

coastal waters.



The ridge aloft will continue to erode during the next few days,

as a broad mid to upper level trough will become amplified and

move eastward across the west Atlantic. This trough is to linger

just west of the region through Tuesday thereby increasing

instability aloft over the northeastern Caribbean. At lower

levels, a high pressure ridge north of the area will continue to

move eastward resulting in light to moderate east southeast winds

through Tuesday. With this scenario and based on most recent model

guidance, still expect good tropical moisture transport across

the region from the east southeast at least until the middle of

the upcoming week.



As a result, passing showers embedded in the east southeast wind

flow will remain likely across windward areas during the morning

hours, followed by showers and possibly an isolated thunderstorm

developing over and north of the Cordillera Central each afternoon.

Some of the showers and thunderstorms will be enhanced, leading to

periods of locally heavy rainfall. Therefore urban and small stream

flooding as well as rapid rises along some of the major rivers and

their tributaries will remain possible each afternoon. The

prevailing low level southeast wind flow will also support warmer

temperatures along the northern half of Puerto Rico through at least

midweek. Recent dust aerosol product and guidance also continued to

suggest the intrusion of some Saharan dust across the eastern

Caribbean by Tuesday and Wednesday.



.LONG TERM...Wednesday through Sunday

The area will remain under the influence of an upper level high

pressure, which after Tuesday will remain rather close to the

eastern Caribbean south of the local area. High pressure at 700

and 500 mb also remains east southeast of the area through at

least Sunday, and the subsidence generated will bring in drier

air at those levels. The GFS has been very inconsistent about

moisture levels to be expected in the local area. Only yesterday

it showed more moisture over the following weekend than was

expected tomorrow (Monday), but this is no longer the case and

columnar moisture over San Juan is no longer expected to exceed 2

inches after Monday of this week. Since the plume of moisture out

of the equatorial regions is pushing northward over Hispaniola and

eastern Cuba for most of the week now, am accepting this latest

change and have lowered expectations for rain here after mid week

this week. Confidence level, however, is only medium at this

time. Although the plume does draw closer to the local area late

in the week and over the weekend. At least for now, the threat of

widespread heavy rain has been postponed beyond mid week next

week.



That said, however, there will be sufficient heating and moisture

to generate some early morning showers over the local waters and

the southeast coasts and slopes of Puerto Rico and daily afternoon

showers and thunderstorms over the northeastern two thirds of

Puerto Rico. Urban and small stream flooding would be expected

where these showers are the heaviest.



&&



.AVIATION...VFR conds expected til 14/16Z with brief VCSH across the

local terminals. Sfc wnds fm the SE less than 10 KT become ESE

aft 14/14Z at 10-15KT and slightly higher with sea breeze

variations. Between 14/17Z-14/22Z...locally and diurnally induced

SHRA/TSRA possible across central and W-NW PR with mtn

obscurations and VCSH/VCTS at TJMZ/TJBQ/TJSJ and brief MVFR conds

psbl mainly at TJBQ.





&&



.MARINE...Models may still be overdoing the winds Wednesday and

Thursday but are now only expecting borderline small craft

conditions for seas over both the Atlantic and Caribbean waters.

Although this remains a possibility, the most likely seas will be

up to 6 feet peaking on Thursday.





&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 89 77 90 76 / 20 30 40 40

STT 86 78 86 78 / 20 30 30 50

Area Forecast Discussion

National Weather Service San Juan PR

458 AM AST Tue May 16 2017



.SYNOPSIS...Recent satellite imagery suggests a fairly high concentration

of Saharan dust spread across the region today. Expect lesser amounts

of suspended dust particulates and a cleaner air mass Thursday and

during the rest of the work week. The mid to upper level ridge will

maintain its hold and aid in suppressing convective development across

the region. Surface high pressure ridge will continue to build and

spread across the west and central Atlantic while maintaining moderate

east southeast trade winds across the northeastern Caribbean.



&&



.SHORT TERM...Tuesday through Thursday...

Mid to upper ridge will continue to hold across the eastern/southeastern

Caribbean through Thursday. While at the same time an upper trough lingers

over the western/central Caribbean and across La Hispaniola. Surface

ridge will continue across the eastern/central Atlantic promoting

east to southeast trades and above normal temperatures across the coastal

areas of Puerto Rico. The heat index can range from the high 90s to

the low 100s across the northern coastal areas of Puerto Rico today.

A surface ridge is expected to enter the western Atlantic and build

north of the area by late Wednesday turning winds more from the east.

A weak front will linger/dissipate between the two highs while remaining

north of the area late in the forecast period.



Dry air at mid levels and Saharan dust will continue across the forecast

area at least through early Thursday creating hazy skies. This, in combination

with synoptic upper level pattern of trof across Hispaniola and ridge

over the eastern Caribbean basin will lead to diurnally induced convection

over portions of the northwest quadrant of mainland PR each afternoon.

Limited shower activity is expected across the rest of the island and

the USVI`s other than streamers with light rainfall amounts developing

downwind of the small islands.



.LONG TERM...Fri thru Tuesday...

The mid to upper level ridge will hold across the forecast area through Friday

but will erode over the upcoming weekend as a polar trough will move

across the west Atlantic and north of the region. As the ridge erodes,

low level moisture transport and precipitable water is forecast to slightly

increase once again across the forecast area. In the low levels, high

across the western and central Atlantic will be the dominant weather

feature and is expected to hold in place through the forecast period.

This will result in moderate east to southeast trade winds.



Therefore, expect a mostly seasonal weather pattern with periods

of passing late evening and early morning showers across the coastal

waters and windward side of the islands, followed by mainly locally

and diurnally induced afternoon convection mostly over parts of

the central interior and west sections of Puerto Rico. However,

model guidance does suggest occasional surges of moisture associated

with weak easterly perturbations moving across the region late Saturday

through Sunday and another Sunday through Monday. This should slightly

increase the chance for showers and possibly isolated afternoon thunderstorms

across the western interior and northwest Puerto Rico. Elsewhere,mostly

fair weather and sunny skies is expected with limited shower activity.

Near normal temperatures can also be expected during the long term

period which should be generally in the mid to high 80s in most

areas.



&&



.AVIATION...Mainly VFR conditions expected to prevail across all

terminals for the next 24 hours. HZ skies due to Saharan dust will

continue across the flying area, but visibility expected to remain

P6SM. Brief SHRA/-TSRA possible between 18z-22z near the vicinity of

TJBQ. Trade wind -shra can lead to sct/bkn cigs btw FL030-FL050

across the rest of the terminals. TIST/TISX are reporting false

bkn/ovc low CIGS. Winds below FL100 fm the ESE at 12-22 kts...bcmg

West and increasing with height. Sea breeze variations across W/NW

PR expected after 15z.



&&



.MARINE...Seas increasing up to 6 feet across the Atlantic waters,

offshore Caribbean waters and local passages today. Winds of 10 to

15 knots increasing to 15 to 20 knots by Wednesday.



&&



.CLIMATE...The dominant southeasterly trade winds will result in above

normal temperatures and moderate to high heat indices along portions

of the coastal areas of the islands, with high temperatures reaching

the low 90s in some areas today.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 92 78 90 78 / 20 10 20 10

STT 87 79 88 78 / 20 20 20 10

Area Forecast Discussion

National Weather Service San Juan PR

433 AM AST Thu May 18 2017



.SYNOPSIS...Lesser concentration of Saharan dust was observed across

the region, as the dust particulates continued to diminish. Overall

limited shower activity is expected for the next several days, as

a high pressure ridge will dominate the local weather pattern. A

predominantly dry and stable air mass with mostly sunny skies is

therefore expected to prevail. Increasing trade winds is forecast

today and into the weekend as the surface high pressure will continue

to tighten the local pressure gradient.



&&



.SHORT TERM...Today through Saturday...Ridge aloft will continue

across the eastern Caribbean basin. Saharan dust is expected to continue

over the forecast area today. These two features will result in a dry/fair

weather pattern across the islands. Shower activity will be limited

to brief trade wind showers across the USVI and sections of eastern

PR, followed by shallow afternoon convection over western PR. A trade

wind surge will create breezy conditions over the waters and coastal

areas of the islands. Max temps should reach the upper 80s to lower

90 degrees across the coastal and urban areas of the islands, dropping

to the mid-high 70s during the overnight hours.



.LONG TERM...Recent model guidance still suggests a slight erosion

of the mid to upper level ridge as a polar trough crosses the west

and central Atlantic. On Sunday, a high pressure ridge will enter

the southwest Atlantic and build eastward over the forecast area.

This will remain the dominant weather feature and consequently maintain

mostly fair and stable weather conditions across the region for most

of next week. The surface high pressure will be reinforced on Sunday,

as a cold front and associated weak trough dissipates across the central

Atlantic and north of the region. An easterly pertubations is forecast

to move across the eastern Caribbean late Sunday through Monday of

next week. By Tuesday, expect decreasing moisture transport and increasing

trade winds, with a gradual shift to southeast during the remainder

of next week. This is in response to the surface high shifting further

into the central Atlantic. Model guidance also suggests much warmer/hotter

daytime temperatures, especially along the northern half of Puerto Rico.

Another round of Saharan dust is forecast to arrive across the region

by early next week.



A quick surge of moisture accompanying a weak easterly perturbation

may bring additional low level moisture and showers to the region

late Sunday through Monday. This so far appears to be of short duration

with no major rainfall accumulations expected. No significant weather

feature is forecast to affect the region as mostly fair weather and

sunny skies is forecast at this time. Diurnally induced afternoon convection

should be focused mainly over parts of the central interior and interior

and west sections of Puerto Rico, with mostly streamer- like afternoon

convection over parts of the east sections including the San Juan metro

area. Expect limited shower activity elsewhere.



&&



.AVIATION...Mainly VFR conditions expected to prevail across all

terminals for the next 24 hours. HZ due to Saharan dust but vsby

P6SM. SHRA possible between 18z-22z near the vicinity of TJMZ.

Surface winds from the east at 10-15 knots with higher gusts in

the mid 20s after 14z.





&&



.MARINE...Small craft should exercise caution as the mainly wind

driven seas will be up to 6 feet across the local waters and winds

will be up to 20 Knots.



There is a high risk of rip currents across the northern coast of

Puerto Rico and Culebra, and moderate risk across most of the remaining

beaches in Puerto Rico, Vieques, and Culebra. For the USVI, there is

a moderate risk of rip currents across most of the beaches around the

islands.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 88 78 87 77 / 10 20 20 20

STT 89 78 87 78 / 10 20 20 10