Puerto Rico Weather

Area Forecast Discussion

National Weather Service San Juan PR

523 AM AST Wed Mar 15 2017



.SYNOPSIS...

A mid to upper level ridge will continue to result in stable

weather conditions through the workweek. At the surface, a trough

is forecast to moves from the east into the local Caribbean waters

by early Thursday morning. As this trough reach the islands

surface moisture, clouds and trade wind showers are expected to

increase somehow. However, a fair weather pattern is expected to

dominate most of the time through this period.



The ridge pattern aloft is forecast to weakens by the upcoming

weekend into next week. A surface low pressure system and its

associated cold front is expected to moves northwestward across

the Northwestern Atlantic early this weekend.



&&



.SHORT TERM...

High pressure aloft drifts slowly eastward over the

Leeward Islands today through Saturday. Underneath several short

wave troughs move through the area, one on Wednesday night and

Thursday and the other late Friday night. Each will carry an

increase in clouds and showers. High pressure in the northeast

central Atlantic today will be reinforced by additional high

pressure invading the western Atlantic later in the week. This will

maintain moderate to fresh east northeast to east southeast trade

winds across the area. Before the first surface trough moves into

the area, however, drier air will prevail and there will be weak

capping at 700 mb.



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

At the surface, a low pressure system and associated frontal

boundary is expected to move over the Northwestern Atlantic. The

ridge aloft is forecast to weakens as a mid to upper level trough

swing by the Atlantic waters by the end of the weekend into next

week. If this weather pattern is correct, showers and cloudiness

are forecast to increase as instability and surface moisture

increase over the islands. Model guidance are suggesting moisture

pooling above the normal values for this time of the year, as

well as the possibility of thunderstorm activity by early next

week.



&&



.AVIATION...

Moisture associated with a surface trough will move into

the Caribbean sea south of the forecast area btwn 15/18-16/00z

spreading sct SHRA across the area. Brief periods of MVFR are

possible at TKPK, and at TJMZ aft 15/18z. Expect mtn obscurations

after 15/16z. SHRA are also expected to develop ovr west and

northwest PR aft 15/18z. Winds NE-E 10 to 20 kt up thru FL200.

Maximum wind west 40 kt at FL410.



&&



.MARINE...

Buoys across the coastal waters of the islands are indicating

seas between 3 and 5 feet and easterly winds around 10 knots.

Small craft operators should exercise caution across the offshore

waters and Caribbean Passages due to seas up to 6 feet. In

addition, a small craft advisory is in effect for the Atlantic

Offshore waters and Anegada passage from this evening.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 86 74 87 75 / 10 40 40 40

STT 85 74 84 73 / 10 40 40 40

Area Forecast Discussion

National Weather Service San Juan PR

508 AM AST Fri Mar 17 2017



.SYNOPSIS...A mid to upper level ridge across the area will drift

east and erode today through Sunday allowing a cold front to

approach the area from the northwest. Although trade winds will

continue during the entire period, flow will become more

southeasterly during the week next week and moisture will steadily

increase tonight through Monday and again on Friday and Saturday

of next week. This will increase the chances and coverage of

showers and allow thunderstorms to develop next week.



&&



.SHORT TERM...Today through Sunday

Under a mid to upper level ridge pattern a mostly fair and stable

weather pattern is expected to continue across the local islands

this morning through at least early Sunday. However, small areas of

moisture embedded in the trades may reach the local islands from

time to time to produce brief passing showers across the U.S.

Virgin Islands and eastern sections of Puerto Rico each morning.

Locally induced afternoon showers are also possible across western

and interior sections of Puerto Rico during the afternoons due to

sea breeze convergence. Surface high pressure across the central

Atlantic and a frontal boundary north northwest of the area will

continue to promote an easterly wind flow across the region today.

Winds are expected to become east northeast on Saturday as the

frontal boundary remnants move across the local Atlantic waters.

Therefore, seasonable temperatures will continue to prevail today

with pleasant temperatures expected on Saturday. The chance for

shower activity will increase late Sunday and early next week as

the ridge aloft erodes and the frontal remnants reach the region.



.LONG TERM...Sunday night through Saturday

Low pressure will move off the eastern coast of the United States

on Saturday evening. The cold front that accompanies it will

reinforce the stalled frontal boundary that will have stalled

across the windward passage on Monday. This will enhance the

upward vertical motion ahead of the front over the area and begin

to pull moisture in from the tropical western Atlantic possibly as

early as Sunday afternoon. Current model solutions do not bring

the front or its associated shearline over the forecast area but

the increased moisture and dynamics are expected to generate

isolated thunderstorms and increased shower activity mainly Monday

and Tuesday and Friday and Saturday. Moisture in the GFS solution

peaks either Friday afternoon or Saturday of next week depending

on the model cycle, but this should be the wettest period of the

week. It is too early to tell if flooding could result but some

local urban and small stream flooding should be expected on Monday

and Tuesday and again on Friday and Saturday of next week.



&&



.AVIATION...Mostly VFR condition expected across the local

flying area. VCSH are possible this morning across the Leewards,

USVI and eastern PR taf sites. Afternoon convection will cause

SHRA development around TJMZ and TJBQ. Winds will continue from

the east with sea breeze variations at 10-15kt today, decreasing

and becoming more from the ENE after 17/23Z.





&&



.MARINE...Models have been over estimating sea heights, but buoy

41043 has remained over 7 feet for some time now due to easterly

winds. Expecting seas to increase tonight and Saturday in response

to stronger winds, but subside by Sunday. Seas will likely remain

7 feet or better in the northern part of the outer Atlantic zone

through Sunday. Seas will also likely return by mid week next

week.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 86 75 85 74 / 20 50 50 50

STT 84 73 84 74 / 30 50 50 50

Area Forecast Discussion

National Weather Service San Juan PR

516 AM AST Sun Mar 19 2017



.SYNOPSIS...Increasing moisture, the presence of a cold front to

our north, a subtropical jetstream that holds just to our north

leaving us under favorable upper level dynamics will all

contribute to an increasingly wet scenario for Puerto Rico and the

U.S. Virgin Islands. Rainfall amounts should be highest on

Saturday, but rain is expected in many areas both early and late

in the week.



.SHORT TERM...Today thru Tuesday...

For the rest of the overnight and early morning hours, passing

showers with brief gusty winds can be expected across the local

waters, as well as along portions of the north and east coastal

sections of the islands. During the afternoon hours, the

prevailing east southeast winds should steer diurnally induced

shower activity across the interior and northern half of Puerto

Rico including portions of the San Juan Metro area. Some areas of

heavy rainfall will also be possible in the northwest. Mainly

isolated showers are expected across the U.S virgin islands during

the afternoon.



The mid to upper level ridge will continue to erode as a broad

polar trough will become amplified and move eastward across the

west and central Atlantic through Tuesday. The subtropical jet

will round the base of this trough Monday through Tuesday placing

the region on the divergent and unstable side of the jet max.

Gradually increasing pooling of moisture and low level convergence

is still forecast beginning later this evening through the early

part of the upcoming week. This is in response to the frontal

boundary northwest of the region and an associated induced trough

which will develop and lift across the region Monday through

Tuesday. This overall pattern will result in the easterly winds

becoming more south southeasterly by Monday, then east southeast

once again on Tuesday. Weather conditions will become fairly moist

and unstable on Monday through Tuesday, with favorable conditions

aloft for increased shower activity and enhanced convective

development across the forecast area.



&&



.LONG TERM...Wednesday through Monday 27 March

On Wednesday a weak high pressure ridge will be found in place

enabling easterly trade winds of moderate to fresh intensity to

continue. That ridge will give way before a strong high pressure

moving out of the eastern United States late Thursday. It will

give another push to the front to our northwest and reinvigorate

the easterly trade winds again through the upcoming weekend. This

will maintain the flow of moisture over the area. An upper level

trough will move from Cuba on Wednesday to just north of Puerto

Rico on Sunday but will flatten out considerably as it does so.

The associated sub-tropical jet just north of us will remain

north of us during the entire period but will destabilize the

atmosphere around us on account of our being in the divergent

right entrance region. Moisture will have peaked on Tuesday but

diminishes only a little on Wednesday and Thursday and will rise

considerably late Thursday and early Friday due to the moisture

flow mentioned earlier. The GFS has been consistent in bringing

precipitable water with values of 1.8 to 2.0 inches early Friday

through beyond Monday of the following week. This will bring a

considerable amount of rain to the area should the forecast hold.

It is too early to determine if conditions are conducive for flash

flooding but localized urban and small stream flooding are

certainly possible with the forecast conditions. We continue with

isolated thunderstorms during the week as the inversion is

expected to be removed by Wednesday. The atmosphere becomes very

moist in nearly the entire column beginning Thursday and cloudy or

mostly cloudy conditions should prevail into early next week.



&&



.AVIATION...Mostly VFR conds at all terminals til 19/15Z. SFC

wnds lgt/vrb becmg E-SE 10-15 kts aft 19/14z...except for local

sea breeze variations. Til 19/15z...Isold to Sct passing SHRA ovr

the coastal waters btwn PR and the nrn Leewards islands...SCT-BKN

lyrs nr FL025...FL050... FL100...with VCSH at most of the local

terminals except TJMZ. Mtn top obscr ovr E PR til 19/14z. Fm

19/17z-19/22z... SHRA dvlpmnt psbl ovr ctrl mtn range and NW PR

with VCSH at TJBQ/TJMZ/TJSJ with MVFR psbl.





&&



.MARINE...Winds and seas are diminishing and all small craft

advisories should be down by 2 AM AST Monday. The system now in

the western Atlantic and its associated cold front will send

northerly swell into the area on Wednesday. Seas may reach 7 feet

in the Atlantic waters and passages. Then the newly refreshed cold

front to our north will begin to send much stronger swell into

the area Friday night. Seas of 10 feet or more are still possible

with this system.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 86 73 85 75 / 30 40 50 50

STT 83 73 82 72 / 50 50 50 50



&&

Area Forecast Discussion

National Weather Service San Juan PR

447 AM AST Tue Mar 21 2017



.SHORT TERM...Tuesday-Thursday...Overnight showers were mainly

observed over the Atlantic waters and over portions of eastern PR.

However, no significant rainfall accumulations were observed. It was

mostly clear across the USVI with temps in the low 70s across

coastal areas. An induced surface trough moving across the Caribbean

waters will enhance afternoon convection along the mountain ranges

of PR this afternoon. As soils are already saturated due to

yesterday`s rains, any period of heavy or prolonged rainfall across

the interior and north of the Cordillera will lead to urban and

small stream flooding. Upper level trough will weaken and associated

sfc front will linger across the Atlantic waters. Afternoon

streamers and passing showers are expected mainly across the USVI.



Forecast soundings are indicating light steering winds from the east-

southeast around 10 kts through Thursday. In addition, another mid

to upper level trough will move from the west late Wednesday into

Thursday enhancing upper level dynamics across the region. So any

additional afternoon shower development over land areas will continue

to pose a threat of at least urban and small stream flooding through

the short term period. Associated low level shearline is forecast

to enhance more moisture and favorable conditions for more rainfall

late in the week and into the weekend.



.LONG TERM...late Thursday-next Tuesday...High amplitude trough

is forecast to deepen and extend across the Greater Antilles into

the west and central Caribbean Thursday through Friday. This will

gradually increase instability aloft and enhanced upper level

divergence across the region. A subtropical jet max is forecast to

round the base of the upper trough and lift northeastward just

north of the forecast area. In the low levels, a broad inverted

surface trough will linger across the central and eastern

Caribbean. As a result, a moist southeasterly flow will persist

through Friday and into the weekend. Therefore a much wetter

pattern with enhanced tropical moisture advection is forecast for

the next several days. Good moisture convergence along the

approaching frontal boundary, and surface trough along with the

upper level instability will favor increased potential for

enhanced convection across the region through the weekend and at

least until Tuesday of next week. Thereafter winds are forecast to

become more northeasterly as surface high pressure ridge will

spread across the west Atlantic. Until then, expect periods of

late evening and overnight passing showers along portions of the

north and east coastal sections of the islands,followed by afternoon

convection with enhanced shower activity particularly across the

interior and northern half of Puerto Rico. The potential for periods

of locally heavy rainfall with minor urban and small stream flooding

in isolated areas will therefore remain high across portions of the

islands especially Puerto Rico.



&&



.AVIATION...Mostly VFR early in the forecast period across all

terminals. However, weak trough moving fm the Leeward islands into

the eastern Caribbean will create SCT-BKN cigs and enhance diurnal

convection across the islands in the afternoon. Therefore, tempo MVFR

conds possible mainly over mainland PR terminals between 16z-22z.

Low level winds will continue at 6-15 kts with sea breeze variations

after 14z.



&&



.MARINE...Seas generally 3 to 5 feet are expected overnight but increasing

gradually during the rest of today. Small craft advisory will go into

effect later tonight for the offshore Atlantic waters as seas will approach

7 feet due to increasing trade winds and a northerly swell reaching

the local waters. A larger northerly swell is still forecast to arrive

and spread across the Atlantic waters and local passages will by late

Friday.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 84 74 86 75 / 30 30 30 20

STT 85 75 84 75 / 30 30 30 30

Area Forecast Discussion

National Weather Service San Juan PR

509 AM AST Thu Mar 23 2017



.SHORT TERM...Today thru Saturday...Deep southerly wind flow will

continue to pool moisture across the forecast area. As a prefrontal

trof establish over the islands and an upper level trof pattern

evolves from the west in the short term period. For today...through

the morning hours, showers will continue to develop over the Caribbean

waters and move over the USVI and the southern/eastern portions of

PR. During the afternoon hours, high res models are indicating shower

development over the north/northwest quadrant of PR. Shower activity

will remain high through the forecast period across the Atlantic waters

due to a meandering shearline between Hispaniola and the Mona Passage.



Better moisture advection over the islands is expected on Fri

through Saturday and in combination with good divergence aloft...

scattered to numerous showers and isolated thunderstorms are expected

each day. Forecast soundings are indicating a gradual increase in

PWAT from around 1.70 inches today to near 2 inches on Saturday.

Localized urban and small stream flooding is very likely these two

days.



.LONG TERM...Sunday-next Friday...The mid to upper level trough is

forecast to deepen and extend southwards into the west and central

Caribbean through early Sunday. The trough will then lift further

north into the west and central Atlantic. A developing surface low

north of Hispaniola with the associated trough will continue to induce

a moist southerly flow and unstable weather pattern across the region

until Monday or early Tuesday. Winds are to become more northerly

by late Tuesday through the end of the week, as surface high pressure

will build across the western Atlantic and north of the region. By

Wednesday of next week through Friday, north to northeast winds

should prevail and this should bring much drier and stable condition

to the region. However brief early morning passing showers cannot

be ruled along the north coastal areas due to the prevailing northerly

winds. This will be followed by isolated to scattered afternoon shower

activity each day.



In the meantime...Deep layered moisture advection and instability

aloft due to upper trough and subtropical jet maxima will persist

over the northeastern Caribbean through Sunday. Enhanced early

morning and afternoon convection will be likely across the islands

and coastal waters. The upper trough and subtropical jet maxima will

fill and lift north of the region by late Monday and Tuesday resulting

in less favorable conditions aloft for enhanced convection and a gradual

decrease in morning and afternoon shower activity. The potential for

periods of locally heavy rainfall with minor urban and small stream

flooding as well as quick rising of water levels along rivers and

guts will remain high across portions of the islands at least until

Monday of next week due to saturated soils and the expected unstable

weather conditions.



&&



.AVIATION...SHRA will continue across the regional waters and btw

the eastern PR and the USVI. These showers can result in tempo MVFR

conds at TIST/TISX. Sct-bkn cigs btw FL030-060 expected to continue

with mountain obscd over PR through the fcst period. Additional SHRA

is expected during the afternoon and periods of MVFR conds cant be

ruled out at TJSJ/TJBQ/TJMZ. Iso TSTMs possible after 24/00z over

the offshore waters. Southerly winds around 10 kts expected blo

FL100...bcmg SW-W above and increasing w/height. VFR expected for

much of the fcst period at TNCM/TKPK.



&&



.MARINE...Recent buoy observations continue to suggest seas up to

7 feet across the offshore Atlantic waters. As a result, the Small

Craft advisory has been extended until 10 am AST this morning. A larger

northerly swell generated by the developing low is expected to impact

the Atlantic waters and local passages by late Friday. This will again

create hazardous and building seas over the weekend. Please refer to

the latest Coastal Waters Forecast (CWFSJU) and Marine Weather Message

(MWWSJU) issued by WFO San Juan PR for additional information on the

local marine hazards.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 86 74 85 75 / 40 50 70 50

STT 83 73 82 73 / 30 60 60 60

Area Forecast Discussion

National Weather Service San Juan PR

517 AM AST Sat Mar 25 2017



.SYNOPSIS...Deep layered moisture and trof pattern aloft will

maintain an unsettled weather pattern through the rest of the

weekend. A surface trough and a developing low to the north of

Hispaniola and the Mona Passage will continue to promote a

moderate southerly wind flow over the forecast area. At least

through the weekend the potential for urban and small stream

flooding will remain high across the islands. The low and a

building high across the Western Atlantic will promote northwest

to northerly winds by early next week.



&&



.SHORT TERM...Today through Monday...



A shear line across the Atlantic waters in combination with a

developing low pressure system just north of Puerto Rico will

maintain a very moist and unstable southwest wind flow across the

region until at least Sunday. At the same time an upper level trough

extending from the central Caribbean northward across Jamaica and

Cuba and then over the Atlantic waters has maintained an associated

jet over the Atlantic waters to the north of the region. These

features will aid in the development of showers and thunderstorms

across the region today an until early the upcoming week. Abundant

tropical moisture embedded in the wind flow will continue to bring

showers and thunderstorms across the Caribbean waters and then

across Puerto Rico and the U.S. Virgin Islands today.



Early this morning Doppler radar indicated scattered to numerous

showers moving from the Caribbean waters, north northeastward

across south central and eastern sections of Puerto Rico as well

across Vieques, Culebra and the U.S. Virgin Islands. Urban and

small stream flooding are possible today and Sunday across Puerto

Rico and the U.S. Virgin Islands. Drier air will filter across the

region on Monday, but moisture will linger across the region to

produce some showers especially during the afternoon hours.



.LONG TERM...Tuesday Through Saturday...



Surface low is forecast to move north of the islands through early

next week across the Central Atlantic as a building ridge across

the Western Atlantic builds and moves north of the islands by

late in the week. This will result in a northwest to northerly

wind flow through the middle of the week. As the low pulls away,

moisture content is expected to diminish quickly over the islands

but moisture content will remain high over the Caribbean Sea. At

the moment, best chance for showers are expected between

eastern PR and the USVI on Tuesday. At upper levels another short

wave trof is expected to move on Wednesday. Then a ridge will

build across the Caribbean basin. This in combination with a cool

northerly wind flow due to the surface high will promote drier air

and seasonable weather conditions across the islands.



&&



.AVIATION...SHRA/TSRA will produce periods of MVFR or even IFR

conditions across the Leewards, USVI, TJPS and TJSJ taf sites until

at least 25/16z. VCSH expected across the rest of the local flying

area this morning. Mountain obscurations will continue over PR thru

26/00Z. Bands of moisture with embedded +RA and TSRA will move

occasionally over the local flying area this afternoon to produce

periods of MVFR conditions across most taf sites.



&&



.MARINE...A large northerly swell will fill in across the local

passages and Atlantic waters through Sunday. Small craft

advisories are in effect. Seas should range between 8-10 feet

across the offshore Atlantic and under 8 feet elsewhere across the

passages and the northern coastal waters of the islands. A high

surf advisory is in effect for the northwest through northeast

coast of PR and a high rip current risk is also in effect for the

same areas including northern Culebra and northwest St. Thomas.

Beach goers are urged to avoid these coastal areas through the

rest of the weekend.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 86 75 86 75 / 50 20 50 40

STT 81 74 82 75 / 20 50 50 50