Puerto Rico Weather

Area Forecast Discussion

National Weather Service San Juan PR

353 AM AST Wed Mar 29 2017



.SYNOPSIS...A surface high across the southwest Atlantic will

push the surface low to the northeast of the region further

northeast well away from the local islands. As this happens, the

local winds will shift to the north northeast today. Lingering

moisture across the region will combine with local effects to

induce the development of showers and possible thunderstorms along

and south of Cordillera Central today. Winds are expected to

become more easterly by the weekend as the surface high drift

eastward while weakening. North swell is expected to affect the

local waters late Wednesday and Thursday.



&&



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

Partly cloudy skies prevailed across the local islands overnight.

Some light passing showers were seen across the Caribbean coastal

waters. Local Area remains under the influence of a surface low

pressure system which was located several hundred miles northeast of

the area. Trailing moisture associated with this feature will

continue to aid in the development of showers and possible

thunderstorms mainly over the Cordillera Central of Puerto Rico. The

difference today it is that the wind has shifted northerly. As a

result,shower activity will be focus mainly over the southern slopes

of Puerto Rico.



As the aformentioned area of low pressure continue to move away from

the area, a drier airmass is expected to encompass the region

Thursday and Friday as a high pressure system builds across the

western Atlantic.



.LONG TERM...Saturday through Wednesday...

A weak surface high pressure is expected to develop across the

central Atlantic early in the weekend to maintain an easterly trade

wind flow across the local islands Saturday and Sunday. At the same

time a surface low emerging across the northeastern United States

seaboard will push the surface high eastward while weakening. As

this happens patches of moisture associated with a frontal

remnants will combine with local effects both days to produce an

increase in cloudiness and shower activity across Puerto Rico and

the U.S. Virgin Islands during the weekend, but at this time not

widespread or significant precipitation is expected during this

period.



As the aforementioned surface low and associated frontal boundary

moves northeastward toward the north central Atlantic, another

stronger surface high is expected to develop and drift across the

western Atlantic. This feature will bring an east northeast trade

wind flow across the forecast area late Monday through at least

Wednesday. An upper level ridge is expected to build and

strengthening over the northeast Caribbean during the weekend and

is expected to persist over the region through at least Wednesday.

This feature will inhibit the development of widespread or deep

convection across the local islands during the forecast period,

but moisture embedded in the trades will continue to combine with

local effects to produce some shower activity across western and

interior Puerto Rico each day.



&&



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

TAF sites through at least 29/16z. Periods of MVFR conditions can be

expected across TJPS and TJMZ between 29/16z through 29/22z in SHRA.

Low level winds will be mainly north and northwest at 10 kts or

less.



&&



.MARINE...Seas of 3 to 5 feet will continue to prevail across

the Atlantic waters, with seas 2 to 4 feet across the Caribbean

waters. A moderate risk of rip current will continue across the

Atlantic shoreline of Puerto Rico today and tonight. A northerly

swell will arrive across the local waters late Wednesday into

Thursday with seas increasing up to 6 feet.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 84 75 84 74 / 20 10 10 10

STT 84 74 85 73 / 40 20 20 20

Area Forecast Discussion

National Weather Service San Juan PR

513 AM AST Fri Mar 31 2017



.UPDATE...Brief udpate to include Fire weather section.



&&



.FIRE WEATHER...Relative humidity will reach critical values

today. As a result, A fire weather statement (RFD) has been

issued for the southern slopes of Puerto Rico.





&&



.PREV DISCUSSION... /issued 456 AM AST Fri Mar 31 2017/



SYNOPSIS...Surface High pressure will continue to dominates the

local region. Patches of low level moisture associated with an old

frontal boundary will affect the region Saturday. Another high

pressure system is expected to build across the western Atlantic

by Tuesday next week.



SHORT TERM...Today through Sunday...



Surface high pressure system to the north of the local area and a

broad high pressure int he upper levels will create a pattern where

locally induced showers will be the main weather making feature over

PR this weekend with isolated to scattered brief showers over the

waters and around the USVI.



For today, high pressure system north of the local area will

dominate the local wind flow and weather pattern. The local wind

will remain today from the ENE, which will maintain a relatively dry

airmass over the area, limiting the shower development but not

completely inhibiting it. The available moisture will combine once

again with daytime heating and local effects to cause the

development of showers across the interior and western sections of

Puerto Rico this afternoon. Some showers could develop near the San

Juan metro as well. There will be also isolated showers around the

USVI and some may even stream off the islands.



For Saturday, the moisture is expected to increase over the local

area and the winds will shift to a more ESE direction, which will

likely cause variably to mostly cloudy skies as the day progresses.

There will also be afternoon convection across the NW quadrant and

North Central portions of PR and the San Juan metro, as well as

passing showers across the USVI through the day. Saturday looks to

be the day with the best chance of rain in the weekend.



Sunday will still have some moisture, enough to have showers develop

across the areas of sea breeze convergence in PR, which will be

across the NW quadrant of PR due to ESE winds. Isolated showers for

the USVI. Because of the ESE winds and the lower moisture and cloud

cover expected compared to Saturday, this Sunday has the chance of

also being rather warm with temps reaching the upper 80s.



LONG TERM...Monday through Saturday...



Although the remnants of an old frontal boundary are expected to

affect the area Monday, relatively dry and stable conditions are

expected to prevail during the long term period. A high pressure

system is forecast to exit the eastern U.S. and will move across

the western Atlantic by Tuesday. As a result, trade winds are

expected to increase somewhat as pressure gradient tightens.

Overall, pleasant weather conditions are expected.



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

local terminals. The local winds will be mainly from the ENE at

about 10-15KT with sea breeze variations developing after 31/13Z.

Some SHRA development is expected in the afternoon across various

points in PR, which could cause VCSH across the terminals in PR

mainly after 31/17Z. Winds will decrease after 31/23Z still easterly

for the most part but TJMZ and TJPS may observe light and variable

winds thereafter.



MARINE...Northerly swell will continue to create a high rip

current risk across the north facing beaches of PR, Culebra and

St. Thomas. A larger northerly swell is expected to arrive across

the Atlantic waters and passages on Sunday. Small craft operators

should exercise cautions across the offshore waters and passages

due to 6 ft seas.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 84 76 87 77 / 30 40 40 30

STT 86 75 85 75 / 20 10 20 30

Area Forecast Discussion

National Weather Service San Juan PR

451 AM AST Sun Apr 2 2017



.SYNOPSIS...A band of moisture associated with an old frontal

boundary will enhance shower activity mainly over the interior of

Puerto Rico through Monday. Drier air will filter in from the

northeast beginning late Tuesday as high pressure moves into the

central Atlantic.



&&



.SHORT TERM...Sunday through Wednesday Morning...



Rain-free conditions and clear skies prevailed across the local

islands overnight and early this morning. Winds were light and

variable with coastal temperatures in the mid 70s.



A mid to upper level ridge will hold across the local islands with

some weakening expected by midweek. At lower levels, as a high

pressure across the central Atlantic and east of the area moves

eastward, another high pressure will build north of the area by

Tuesday. This will result in east northeast winds early the upcoming

workweek. An area of low level moisture converge will continue to

prevail across the local islands through at least Tuesday with

precipitable water values near the normal range.



Under this pattern expect a seasonable weather pattern with shower

development over central and west Puerto Rico each afternoon due to

diurnal heating and sea breezes. Some showers are also expected in

the vicinity of the San Juan Metro Area today due to the prevailing

east southeast wind flow.



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



Strong upper level ridge will hold through at least Friday. A cold

front is forecast by computer models to exit the U.S. east coast

by Friday and will move southeast during the next weekend. This

cold front is forecast to move closer to the local area at the end

of next weekend. If the forecast verifies, an increase in shower

activity could occur as this front moves near the area.



&&



.AVIATION...VFR conds expected to prevail at all TAF sites through

02/16z. SHRA expected in and around JSJ/JBQ between 02/16-22z with

brief MVFR conds possible. East southeast winds at around 10 knots

with some sea breeze variations expected today.



&&



.MARINE...Seas up to 7 feet and winds up to 15 knots are expected

to continue across the offshore Atlantic waters and local

passages. Seas between 3-5 feet are expected elsewhere. Small

Craft advisories continues in effect.





&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 88 76 86 75 / 20 30 20 30

STT 84 74 85 75 / 20 30 20 30

Area Forecast Discussion

National Weather Service San Juan PR

500 AM AST Tue Apr 4 2017



.SYNOPSIS...Locally induced afternoon showers are expected

each day across west and northwest Puerto Rico with isolated

shower activity elsewhere. Expect warmer temperatures by the end

of the workweek mainly along the northern slopes of Puerto Rico

under east southeast winds. A wetter pattern possible early next

week.



&&



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



The Doppler Radar detected shower activity moving across the Eastern

Municipalities of Puerto Rico and across the surrounding waters of

St Croix, with some of them moving inland at times. Most of the

showers dissipated overnight as a drier air mass moved across the

islands.



Under a ridge pattern and below normal moisture continue to expect

mostly sunny to partly cloudy skies with no shower activity across

most of the islands. However, passing showers from time to time

cannot be ruled out this morning across the windward sections of

Puerto Rico and the U.S. Virgin Islands. Then, showers are expected

to develop downwind from the U.S. Virgin Islands into the eastern

sections of Puerto Rico late in the morning and early afternoon.

Afternoon convection is expected to develop across the interior and

western sections of Puerto Rico due to the diurnal heating and sea

breeze variations. Most of this activity is forecast to dissipate

around sunset. The potential for urban and small stream flooding is

present for the municipalities of the west interior and western

Puerto Rico during the afternoon hours.



In general, a fair weather pattern is expected due to the mid to

upper level ridge at least until mid-week. However moisture

advection will result in passing showers across the windward

sections during the overnight and early morning hours. Then, the

combination of the local effects and available moisture will result

in afternoon convection across the interior and west portions of

Puerto Rico and downwind from the U.S. Virgin Islands each day.



.LONG TERM...Friday afternoon through Wednesday...



As a surface high north of the local islands shifts eastward, low

level winds will become east southeast by Friday and into the

upcoming weekend. At upper levels, a ridge pattern will hold

across the forecast area through the end of the workweek. The

ridge aloft is then forecast to erode Friday and into the upcoming

weekend as a broad mid to upper level trough moves across the

western Atlantic. This feature is expected to amplify into the

central and eastern Caribbean early next week with its associated

surface front/low level moisture lingering across the forecast

area through at least midweek next week. Therefore, based on the

latest guidance, a wetter pattern is possible early next week

under trofiness aloft and moisture associated with the lingering

boundary. Meanwhile, Wednesday Afternoon through at least Friday

continue to expect a seasonable weather pattern with locally

induced afternoon showers across west and northwest sections of

Puerto Rico. As the ridge aloft collapses during the weekend,

there is a potential for afternoon thunderstorms Sat-Sun.



&&



.AVIATION...VFR conditions are expected during most of the FCST

PRD. However, mountain obsc and afternoon showers are expected

across the interior and west portions of PR. These activity could

impact TJMZ/TJBQ btwn 04/18-22z. MVFR/IFR ceiling are possible

during that period. Also, TJPS can expect SCT-BKN ceilings btwn

FL030-FL060 during the afternoon. Winds are expected from the E-NE

below 10 knots til 04/13z, increasing at 10 to 15 kts with gusts

btwn 20 and 30 kts.



&&



.MARINE...A moderate to fresh easterly wind flow will prevail

throughout the week, becoming east southeast by Friday as the

surface high north of the area shifts eastward. A distant low

pressure moving into the northern Atlantic will generate another

northerly swell which will arrive and spread across the local

Atlantic waters tonight. Seas 4 to 6 feet expected today increasing

5 to 7 feet by tonight. There is a moderate to high risk of rip

currents along the Atlantic shoreline of Puerto Rico, Culebra and

northern USVI.





&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 86 77 87 76 / 20 30 30 10

STT 86 76 86 75 / 30 30 30 10



&&

Area Forecast Discussion

National Weather Service San Juan PR

500 AM AST Thu Apr 6 2017



.SYNOPSIS...Fair weather will continue to prevail through Sunday

with locally induced afternoon showers/thunderstorms expected Sat-

Sun. Warmer temperatures possible along the northern slopes of

Puerto Rico under east southeast winds. A wetter pattern possible

next week.



&&



.SHORT TERM...Today through Saturday...



Fair weather conditions prevailed overnight. The skies remained

clear across the south and west portions of Puerto Rico and partly

cloudy over the U.S. Virgin Islands and in the east and north

sections of Puerto Rico. A surge of moisture interacted with the

warm local waters to result in cumulus clouds over the Atlantic

waters. This clouds brought brief scattered showers across the

eastern half portion of the CWA, affecting East Puerto Rico and

the USVI at times.



Although the satellite imagery indicated the presence of approaching

clouds, this activity is expected to diminish during the morning

hours leaving mostly clear skies with limited or no shower activity.

For the afternoon hours, convection across the interior and northwest

portions of PR is possible, as well as downwind from El Yunque and

into the San Juan Metro Area. Elsewhere, mostly sunny skies with

maximum temperatures in the mid to upper 80s along the coastal areas

and between the mid 70s and low 80s in the mountain areas. Most

of the afternoon showers, if any, are forecast to dissipate around

sunset. Weather conditions on Friday should be very similar to

the past few days.



Under a weakening mid to upper level ridge pattern but with below

normal moisture, the frequency of shallow shower activity should

slowly increase through the weekend. As a result expect passing

showers across the windward sections during the overnight and

early morning hours. Then, the local effects combined with the

available moisture will result in afternoon convection with

isolated t-storms across portions of the interior and west Puerto

Rico. In addition, shower development is possible downwind from

the U.S. Virgin Islands.



.LONG TERM...Sunday through Friday...



Early next week, the local weather regime will be dominated by

trofiness at lower and upper levels. Therefore the chance for

showers and thunderstorms will increase next week.



A mid to upper level trough will prevail across the central Atlantic

and into the central and eastern Caribbean Mon-Thu; with its

associated upper low lingering well northeast of the area through

the entire period. At lower levels, an induced trough will dominate

the local islands Sun-Tue as a frontal boundary, which is associated

with the aforementioned trough, stalls northwest of the forecast

area. This feature will enhance the moisture advection early next

week. A drier air mass is expected by Thu as the remnants of the

frontal boundary moves further south.



Therefore, if forecast holds, Sun-Mon continue to expect afternoon

showers and thunderstorms across central and west Puerto Rico. Tue

and Wed with the best moisture advection and the proximity of the

trough the frequency and areal coverage of showers and thunderstorms

should increase. Back in fair weather Thu-Fri.



&&



.AVIATION...VFR conditions expected through the FCST PRD. But, a few

passing showers are expected this morning in/near TJSJ/TIST/TISX.

Then, mountain obsc and afternoon showers remain possible across the

interior and Northwest portions of PR btw 06/18-22z. These activity

could move in/near TJMZ/TJBQ. Calm to light and variable winds,

becoming from the E/ESE at 10 to 20 with higher gusts aft 06/13z.





&&



.MARINE...A northerly swell will continue to impact the local

Atlantic waters and passages throughout the day with swell action

subsiding tonight and into Friday. Small Craft Advisories remains

in effect due to seas up to 7 feet. There is also a high risk of

rip currents along the Atlantic shoreline of Puerto Rico, Culebra

and northern USVI.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 87 75 87 75 / 10 0 10 20

STT 85 74 81 74 / 10 0 20 20

Area Forecast Discussion

National Weather Service San Juan PR

521 AM AST Sat Apr 8 2017



.SYNOPSIS...

The mid to upper level ridge pattern will continue to erode aloft,

as a Polar trough, now over the Western Atlantic, approach the

region. As the trough pattern amplify, weather conditions are

expected to become more conducive for the development of showers

and thunderstorms through the upcoming week. A frontal boundary

is expected over the Western Atlantic Ocean and near Cuba, is

forecast to reach the islands by the upcoming week. As it moves

closer to the region, a pre-frontal trough is forecast to

deteriorate the local weather conditions.



&&



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

Fair weather is expected across the local area in the morning hours

today and on Sunday with only a few brief showers, if any. Locally

induced showers are expected today across the interior of PR into

the north central sections as well as portions of northeastern PR

and the San Juan metro in the afternoon hours. Under the east

southeasterly wind flow, the showers that do develop across the

interior of PR should drift to the NW as the afternoon progresses,

in addition, some showers could stream off the USVI and from the

Luquillo Mountain Range, the latter possibly affecting portions of

the San Juan metro. Slightly higher moisture is expected on Sunday

but the winds are expected to be more easterly, which means that

most of the shower activity on Sunday afternoon should be across the

interior and western interior of PR with some showers affecting

portions of NW PR. The rest of the local area should observe

isolated showers.



The story changes a bit for Monday as deeper moisture and more

favorable upper level dynamics are expected to be present. The local

guidance is currently indicating that more numerous showers and

thunderstorms could be expected on Monday afternoon. However, it

seems as though Monday will have a line of showers moving in even in

the morning hours, slowly moving across the local islands, then, if

the timing is correct, the line of higher moisture will reach Puerto

Rico at the time of max heating, which could cause numerous showers

and a few thunderstorms over Puerto Rico through the afternoon hours

into the early evening hours. Monday looks quite a bit more rainy

than this weekend.



.LONG TERM...

A mid to upper level trough pattern is forecast to dominate the

weather conditions through the workweek. Also, a surface front

and associated moisture are expected to affect the islands

through at least midweek. Model guidance suggest a wet pattern

through much of the upcoming week. Also, a surface low is forecast

to enter the North Western Atlantic. This low is suggested to

move eastward well north of the region, but if the model are

right, this weather pattern will pool tropical moisture from the

South into the islands.



&&



.AVIATION...

VFR conds expected through the forecast period across

the local terminals. Fair weather and light winds expected through

08/14Z. Easterly winds at around 10-15KT after 08/14Z with VCSH

possible across the local terminals as afternoon convection develops

across PR and as SHRA stream off the USVI. Winds to decrease after

08/23Z but continued easterly with ISOLD/SCT SHRA across the local

area which could cause brief VCSH for the USVI terminals and TJSJ.



&&



.MARINE...

Mariners can expect seas below 5 feet and easterly winds mainly

between 10 to 15 knots. Tranquil marine conditions are forecast

through the next few days. In addition, there is a low to moderate

risk of rip current across the islands today.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 85 74 86 75 / 40 30 20 50

STT 85 76 85 75 / 20 20 20 50

Area Forecast Discussion

National Weather Service San Juan PR

445 AM AST Mon Apr 10 2017



.SYNOPSIS...An induced surface trough will move across the U.S.

Virgin Islands and Puerto Rico today. As a result...moisture will

surge giving way to the development of showers and thunderstorms.

Heavy rainfall flooding will be the primary threat today.



&&



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

A good increase in overall moisture is expected today with an

induced trough over the area. There is also an upper trough to our

northwest that will help increase instability over the area,

especially for the afternoon hours. The model guidance suggests that

the highest amount of moisture over the local islands will occur in

the early afternoon hours, which should lead to numerous showers and

a few thunderstorms over several sectors in Puerto Rico, especially

when there is upper level support like there for today and once the

higher moisture combines with the diurnal heating, local effects and

sea breeze convergence. The current forecast calls for numerous

showers and isolated thunderstorms for most of the northern half of

PR in the afternoon with scattered showers elsewhere. This expected

activity could lead to urban and small stream flooding. However, the

USVI should observe mainly isolated to scattered showers.



Tuesday looks somewhat similar with slightly less moisture but still

enough to cause locally induced showers and a few thunderstorms

across the western and central portions of Puerto Rico. Winds are

expected to gradually shift to a more ENE direction for Wednesday,

which would then cause the locally induced afternoon showers to

develop across the interior and SW quadrant of PR. There is less

moisture expected for Wednesday so there is less shower activity

expected, but still some of the showers could be significant.





.LONG TERM...Thursday through Tuesday...Deep layer low north of

Puerto Rico will slowly fill through Saturday while subtropical

jet will become zonal late in the week...extending along the

Tropical Atlantic from Puerto Rico to Africa. As the low pressure

north of the islands dissipates...winds will shift to the east-

northeast in response to a building high pressure over the Western

Atlantic. Looks like the overall moisture will decrease below

normal between Friday and Saturday when operational models suggest

precipitable water values of 1.25-1.5 inches. At the same time...

the mid to upper level ridge reaches it maximum amplitude.



Wetter pattern may return to the local region early next week as

broad polar trough favors moisture transport across the East and

Northeast Caribbean. The exact timing and impacts over Puerto

Rico and the U.S. Virgin Islands are still uncertain.



&&



.AVIATION...VFR conds expected through the overnight hours with

increasing SHRA across the local area today. TEMPO MVFR conds are

likely between 10/15Z and 10/19Z at TJSJ due to +SHRA and low Cigs.

Possible VCTS for TJSJ but left out of TAF due to uncertainty, but

did put VCTS for TJMZ, TJBQ, and TJPS. NMRS SHRA expected today

across PR with a few TSRA. The USVI expects SCT SHRA through the

day. Winds from the ESE at 10-15KT with variations near SHRA.



&&



.MARINE...Surface trough will slightly increase the winds and

seas...especially across the offshore Atlantic Waters. The

hazardous marine conditions will be brief as surface trough moves

away from the region tonight. Seas will return to normal around

3-5 feet on Tuesday. No significant changes in the marine

conditions are anticipated the rest of the week.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 87 74 86 75 / 60 50 50 40

STT 83 74 84 74 / 30 30 40 40