Puerto Rico Weather

Area Forecast Discussion

National Weather Service San Juan PR

515 AM AST Wed Dec 28 2016



.SYNOPSIS...A seasonable weather pattern will continue to prevail

through at least Friday under a mid to upper level ridge and low

level moisture near normal values. Low level moisture may increase

by the end of the workweek and into the upcoming weekend. This

may increase the frequency of passing showers across the local

islands.



&&



.DISCUSSION...Ridge pattern aloft will continue to prevail across

the forecast area during the next several days. Although, there is

a weakening expected at upper levels by the end of the week; the

mid level component will continue to hold through at least next

week. At lower levels, migratory highs north of the area will

continue to promote a generally fresh easterly wind flow through

Thursday. Winds are expected to become moderate on Thursday and

slightly from the southeast Friday as a shearline dissipates north

of the area. The aforementioned shearline may induce a surface

trough across the northeast Caribbean which will result in

moisture pooling across the forecast area late Fri-Sat.



Therefore, continue to expect passing showers across USVI and E

PR in the late evening and early morning hours today through Fri.

The frequency of these showers may increase by the end of the

workweek and the first part of the weekend as moisture pools

across the area. Although convection likely due to sea breeze

convergence, still expect shallow activity due to the lack of

upper level forcing.



&&



.AVIATION...Mostly VFR conditions expected across all terminals

throughout the forecast period. Isolated to scattered passing

showers will continue over the regional waters with some reaching

the Leeward islands, as well as eastern and northern Puerto Rico.

This will create brief -RA/VCSH at times during the overnight and

early morning hours. Winds will continue from the east at 10 to 15

knots with occasionally higher gusts throughout the day. A sea breeze

component will dominate TJMZ and TJBQ during the late morning hours,

but will become more from the east once again in the early afternoon

hours. Trade winds showers will once again bring -RA/VCSH conditions

in the afternoon, especially for the TJSJ, TJBQ, TIST and TISX.



&&



.MARINE...Fresh easterly winds will continue to prevail across

the regional waters through at least Thursday. This will continue

to result in choppy and hazardous seas today and tomorrow with

seas BETWEEN 6 and 8 feet. Seas will briefly subside as the local

pressure gradient weakens by the end of the workweek. A high risk

of rip currents continues for the Atlantic shoreline of PR,

Culebrita Beach and Saint Croix.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 85 77 86 77 / 20 30 30 20

STT 86 77 86 77 / 20 30 30 30

Area Forecast Discussion

National Weather Service San Juan PR

516 AM AST Fri Dec 30 2016



.SYNOPSIS...Showers embedded in the trades are expected at times

across US Virgin Islands as well as eastern Puerto Rico followed

by shallow afternoon convection over northwest Puerto Rico.

Moisture advection still expected as a shearline north of the

forecast area induces a surface trough across the northeast

Caribbean. A fair weather pattern is expected Sunday and into

midweek next week.



&&



.DISCUSSION...Partly cloudy skies were observed across the local

islands during the overnight and early morning hours. Scattered

passing showers were observed over the local waters as well as

US Virgin Islands and eastern Puerto Rico. Overnight minimum

temperatures were generally from 70 to 75 degrees at lower

elevations. Winds were mainly light and variable.



A shearline north of the forecast area will induce a short-lived

surface trough across the local islands which will promote moisture

advection through early Saturday. Although moisture is expected

to increase at lower levels, the mid levels will remain fairly dry.

As the aforementioned shearline and its associated surface trough

dissipates, a broad surface high pressure will build across the

western Atlantic and into the local area. This feature will hold

through at least midweek next week, bringing breezy conditions as

well as patches of low level moisture at times. Ridge pattern aloft

is also expected to strengthen.



As a result, continue to expect passing showers across USVI and E

PR in the late evening and early morning hours. The frequency of

these showers may increase late this evening and Saturday evening

as moisture advects across the eastern Caribbean. Afternoon convection

across west PR is likely this afternoon and Saturday afternoon

due to weaker trades which will allow sea breeze convergence,

but still expect shallow activity due to the lack of upper level

forcing.



A generally fair and mainly stable weather pattern is expected

Sunday afternoon and into midweek next week with trade wind

showers at times.



&&



.AVIATION...Prevailing VFR conds expected through the next 24 hours

across the local terminals. Sct brief SHRA moving across the area

through 30/14Z will continue to cause VCSH across the terminals

except for TJMZ. SHRA development across NW-PR is expected to affect

areas in and around TJBQ and TJMZ between 30/17Z and 30/22Z which

could affect the actual terminals briefly. Winds to continue from

the east at about 10KT through 30/14Z, slightly increasing

thereafter with sea breeze variations developing.



&&



.MARINE...Marine conditions will continue to improve through Saturday.

However, hazardous seas will come back early next week as strong

high pressure builds over the Western Atlantic. A moderate risk of

rip currents continues across most of the local waters.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 86 77 84 77 / 20 10 30 50

STT 85 77 83 77 / 30 20 30 30

Area Forecast Discussion

National Weather Service San Juan PR

535 AM AST Sun Jan 1 2017



.SYNOPSIS...SFC high pressure moving across the western Atlantic

will tighten the local pressure gradient and cause an increase in

the local wind speeds. Patches of moisture will pass through the

local area causing brief showers to pass by. East to ENE winds at

10-20 MPH expected for the next several days. Surface low pressure

will move across the eastern coast of the USA, causing a slight

weakening in the local wind speeds starting on Wednesday as it

pushes the SFC high pressure further to the north and east.



&&



.DISCUSSION...Isolated to scattered showers were observed across

the Caribbean waters overnight and into the early morning hours,

leaving minimal amounts of rain across the USVI and eastern PR

under easterly winds. This pattern of brief showers across the

waters, USVI, and eastern PR is expected for the rest of today.

This is also the pattern that is expected for the next few days

during the overnight and early morning hours. In addition, the

patches of moisture may help the development of showers in the

afternoon across the western sections of PR, particularly over the

areas where there is sea breeze convergence. There is no real

upper level dynamical support for these showers to develop into

something significant enough to cause hazardous flooding.



Late this week, the available moisture will become more constant

and even as opposed to patches of moisture, however the overall

forecast is expected to remain similar, brief showers in the

windward side of PR and the USVI in the nighttime hours and

showers developing in areas of sea breeze convergence in the

afternoon.





&&



.AVIATION...VFR conditions expected to prevail during the

forecast period. By 01/18z...clouds and -SHRA/SHRA is expected to

affect PR/USVI. This will result in VCSH, -SHRA and SCT-BKN CIGS

btwn FL025-FL050. Easterly winds at 5-10 kt increasing 10-20kt

with higher gusts/sea breeze aft 01/13z.





&&



.MARINE...Small craft advisory will go into effect today for most

of the local waters due to an expected increase in winds and seas

starting this morning. Latest model guidance suggests that seas

could increase up to 8 feet across the offshore Atlantic waters

while the rest of the offshore waters and local passages could

observe seas up to 7 feet starting today or tonight and continuing

for the next few days. There is also a high risk of rip currents

across the northern beaches of Puerto Rico and Culebra today.

High risk of rip currents will spread tonight across some beaches

in northern Saint Thomas.





&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 85 75 84 74 / 30 30 30 30

STT 85 74 84 74 / 30 30 30 30

Area Forecast Discussion

National Weather Service San Juan PR

453 AM AST Tue Jan 3 2017



.SYNOPSIS...Winds will weaken somewhat and become more

southeasterly allowing temperatures to warm slightly Wednesday

through Saturday. Otherwise mostly scattered fast moving showers

will continue on and off-through the week. A cold front will

approach early next week.



At upper levels...After a weak ridge passes through today a trough

will move through Wednesday morning. Stronger ridging will

commence thursday and persist until at least early next week.



At mid levels...After a weak trough draws close on Wednesday high

pressure will generally dominate the area until early next week.

The GFS is forecasting a trough passage early Thursday next week.

The best moisture will occur over the weekend and on the approach

of the aforementioned trough Tuesday and Wednesday of next week.



At lower levels...High pressure in the central Atlantic will drift

eastward but leave higher pressure north of the area until early

next week. A frontal boundary will approach the area mid week

next week and much higher pressure will invade the western

Atlantic.



&&



.DISCUSSION...Spotty showers of light to moderate rain dotted the

local waters upstream and along side of Puerto Rico. The showers

were moving at about 25 knots toward the west southwest and

entering eastern Puerto Rico before dissipating. Bands of moisture

will continue over and just north of the area, but the amount of

showers should decrease somewhat during the remainder of the week

as streaks of drier air pass by--especially Wednesday and

Thursday.



Models suggest a warming trend beginning Wednesday morning and

continuing through Friday or Saturday. Winds at 850 and 700 mb

will contain a southerly component during that period so the

warmth will be noticed more by those on the northern side of

Puerto Rico.



The approach of a strong trough and a cold front during the

upcoming week could bring a round of wet and cooler weather. But

more time is needed for models to sort out whether the front can

actually pass through the area. Certainly a large amount of very

cold air will be moving into the western Atlantic early next

week...but it will also stay well north of the area.



&&



.AVIATION...Mostly VFR conditions expected across all terminals

through the forecast period. Brief -RA/VCSH possible at times due to

trade wind showers across the flying area. Surface winds ENE at 10-

15 kts with higher gusts after 03/14z.



&&



.MARINE...Winds and seas will diminish today through Thursday. A

long period swell is expected over the weekend. Breaking waves on

the Atlantic coasts may approach 10 feet then.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 85 74 85 72 / 20 40 20 20

STT 85 73 83 74 / 20 50 20 30

Area Forecast Discussion

National Weather Service San Juan PR

539 AM AST Thu Jan 5 2017



.SYNOPSIS...Ridge aloft will persist through early next week.

Surface high pressure across the Central Atlantic will continue to

promote moderate E-ESE winds through the weekend. A strong polar

trough and associated frontal boundary are forecast to approach

the area by early next week. An increase in moisture and winds

from the NE is expected then.



&&



.DISCUSSION...Short wave trough enhanced the trade wind shower

activity across the Offshore Caribbean waters as it continued to

exit the forecast area during the overnight hours. Isolated

thunderstorms were also noted with this activity. A few showers

made it across the U.S. Virgin Islands and isolated area of

eastern and the southern coast of PR. Between 0.25-0.45 in. were

observed across St. Croix. However, rainfall was not significant

over land areas across PR.



Overall, a fair weather pattern is expected to continue through at

least Sunday. Under ridge pattern aloft...trade wind showers will

continue to bring brief periods of rainfall across the islands and

limited shallow afternoon convection over the interior/northwest

sections of PR. By early next week, a strong polar trough aloft and

associated frontal boundary are forecast to reach the local area.

This will result in breezy conditions under a strong NE wind flow

and increase shower coverage across the islands.



&&



.AVIATION...VFR conds expected at all the terminals through the

forecast period. A few SHRA will move across the flying area but no

operational issues are anticipated today. SE at 10-15 kt will

prevail below FL150.



&&



.MARINE...Seas should continue between 3 to 5 feet and E-ESE

winds at 10-15 knots and locally higher through Friday. A long

period northeasterly swell is forecast to increase seas once again

on Saturday, resulting in hazardous marine conditions and strong

rip currents across the east and north facing beaches of the

islands through the weekend.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 87 74 86 74 / 30 0 10 0

STT 84 74 84 75 / 30 10 10 10

Area Forecast Discussion

National Weather Service San Juan PR

427 AM AST Sat Jan 7 2017



.SYNOPSIS...Mid to upper level high pressure ridge will linger across

the region through most of the weekend. It is however forecast to

erode by late Sunday and Monday as a broad polar trough enters and

becomes amplified across the west and southwest Atlantic. In the

low levels, high pressure centered across the north central Atlantic

will dominate the overall weather pattern through the weekend to

maintain moderate southeast to east trade winds. The surface ridge

is to then weaken on Sunday as the Atlantic high shifts farther

northeast and an induced frontal trough and area of low pressure

develops along a cold front which will enter and move eastward across

the west Atlantic. The cold front and associated frontal remnants is

still forecast to sink southward near to or across the region by the

middle of next week as the area of low pressure develops northeast

of the region.



&&



.DISCUSSION...Moderate easterly winds will continue to transport

occasional patches of low level trade wind moisture and passing

showers across the coastal waters and parts of the islands during

the rest of the overnight and early morning hours. These showers

will be of light to moderate intensity and fast moving and should

gradually diminish by late morning. This will be followed by

mostly sunny and fair weather skies across much of the islands

during the afternoon and early evening hours. Expect this pattern

to mixture of sunshine and clouds with occasional passing showers

to continue for the rest of the weekend.



Model guidance continued to suggest that this overall synoptic

pattern is to change by mid week with increasing instability aloft

and low level moisture convergence across the forecast area. The

aforementioned cold front and area of low pressure along with the

associated deep layered polar trough aloft is forecast to approach

and eventually move across the area while becoming amplified near

to or across the region. For now, during the latter parts of next

week somewhat cooler, and stable weather conditions are expected

following the frontal boundary which should sink south of the region

while dissipating. Regardless of this scenario, the increasing

moderate to fairly strong northeast trades will bring periods of

passing low level clouds and showers mainly across parts of the

north and east sections of the islands each day under the

prevailingand dominant northerly wind flow. Stay tuned as we

will continue to monitor and see how this pattern unfolds.



&&



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

flying area through the next 24 hours. Brief trade wind showers may

move across the Leewards, USVI and TJSJ TAF sites this morning, but

aviation operations should not be affected. Low level winds will

continue mostly from the east at 10-15 knots with occasionally wind

gusts up to 20 knots.



&&



.MARINE...A long period northeast swell has entered the local waters

and Seas will spread across the local waters and all passages. Small

craft advisories will remain in effect for the local Atlantic and

offshore Caribbean waters as well as local passages. Small craft

exercise caution elsewhere except for the near shore waters of west

PR.



Marine conditions will improve by Monday, but is forecast to quickly

deteriorate once again by the Tuesday and Wednesday, as a cold front

and an area of low pressure relocates and develops while lingering

just northeast of the region through the end of the week. This anticipated

pattern should generate large northerly swells across the regional waters

and local passages. Therefore, significantly high Seas and dangerous

surf conditions will remain likely across the forecast area beginning

early Tuesday and spread across most of our waters through at least

the end of next week.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 86 74 85 74 / 20 30 30 20

STT 84 74 84 72 / 20 30 30 30

Area Forecast Discussion

National Weather Service San Juan PR

423 AM AST Mon Jan 9 2017



.SYNOPSIS...An upper level ridge will continue to erode rapidly

today as a deep polar trof amplifies southeastward over the

southwestern Atlantic. A strong surface high pressure moving

across the eastern United States seaboard will push an associated

frontal boundary/shear line across the region late today and

Tuesday. TUTT will develop well northeast of the area early in the

week.



&&



.DISCUSSION...Under a northeast low level wind flow, Doppler

weather radar detected brief isolated to scattered showers moving

rapidly across the USVI, Vieques, Culebra as well as across the eastern

and northern sections of Puerto Rico. This activity will continue

for the rest of the morning hours. No significant precipitation

was observed elsewhere over land areas so far this morning.

Cloudiness is expected to increase across the region today and for

the next several days. This moisture in combination with local

effects will induce the development of scattered showers across

interior, western and southwest sections sections of Puerto Rico

this afternoon.



Satellites images as well as model guidance depicted a deep polar

trof amplifying across the eastern United States. This feature

will continue to amplify southeastward over the Southwestern

Atlantic today and Tuesday. A strong surface high pressure is

expected to develop today over the eastern United Stated

seaboard. As this happens, an associated frontal boundary/shear

line will be pushed across the local islands late today and

Tuesday.



This feature will induce an increase in moisture across the

region for the next several days. Northeast winds are expected to

increase even more tonight and for the next several days. These

northeasterly wind flow will transport areas of cloudiness and

showers across the local islands for most part of the week. A

broad area of low pressure is forecast to develop to the

northeast of the local islands by the end of the week.



&&



.AVIATION...VFR conds across the local flying area durg prd.

However, brief trade wind SHRA and prds of SCT-BKN cld lyrs nr

FL025...FL050...FL090 en route btw islands from time to time. VCSH

across the Leeward islands, USVI and TJSJ taf sites til 09/14Z. Aft

09/17Z...SHRA mainly over ctrl interior and W-SW PR with brief MVFR

psbl mainly with SHRA and CIGS nr FL025. Brief mountain top obscr

ovr parts of central mountain range of PR mainly w/SHRA and few low

clds. Surface winds lgt/vrb bcmg mainly fm E-NE 10-15 kts aft 09/14z.



&&



.MARINE...Seas are expected to deteriorate rapidly tonight. The

combination of a large swell event and increasing winds will

generate dangerous marine conditions from tonight through at

least the next weekend. Small craft advisories will go into effect

as soon as tonight. A High Surf Advisory may be required by early

Tuesday. Mariners and beachgoers should pay close attention to our

local forecast.



&&



.PRELIMINARY POINT TEMPS/POPS...

SJU 83 73 81 73 / 40 40 40 30

STT 84 73 84 73 / 40 50 50 30