SHORT TERM
Tonight through Tuesday...

Sunshine and southerly winds have dominated the weather picture so far. San Juan has already broken its daily temperature record with 95 degrees and many stations along the north central have reached heat indices between 117 to 122 degrees Fahrenheit. The heat advisory along the north central was upgraded to an excessive heat warning. Temperatures elsewhere in the lower elevations ranged from around 90 to the mid 90s. Temperatures in the mid to upper elevations ranged from the mid 80s to the upper 70s respectively.

High pressure at the surface continues in the northeast Atlantic with only a tenuous ridge extending southwest into the northeast Caribbean. Tropical Storm Gordon will continue its westward travel through Monday and has split the ridge so that on Monday a weak high pressure will be found only 400 miles north northeast of San Juan.
This will turn the low level flow more easterly and give a few degrees of relief to the persistent heat we have been experiencing.
Unfortunately, it will likely not be enough, with the high dewpoints we have been having, to end the daily occurrence of heat advisories in the lower elevations. Overall moisture is expected to increase on Tuesday with a slight increase in shower activity. Additionally, instability will reach a bottom on Monday evening with only a slow recovery on Tuesday to limit convective activity in the area.

At upper levels, a ridge over San Juan, Puerto Rico extends about 1000 miles east northeast to its associated high pressure. A lobe of this high pressure will pass north of Puerto Rico to the Dominican Republic by Tuesday morning leaving the local area under subsidence and a drying influence. The high dewpoints represent only a shallow layer and convection tonight through Tuesday will be minimal, although a few afternoon thunderstorms cannot be ruled out over Puerto Rico. A few minor showers will also continue over the local waters.

LONG TERM
Wednesday through Sunday...
//from previous discussion//

An overall dry and stable weather pattern is forecast at least through Wednesday with winds becoming more easterly and gradually diminish. A slight increase in trade wind moisture is forecast by Thursday and rest of the workweek as winds become more east northeast and bands of shallow moisture is brought in across the area from the central and northeast Atlantic. Thereafter the local winds become light and variable with a northeasterly component as the surface high pressure ridge relaxes north of the region. Recent guidance continue to suggest a retrograding Tutt will deepen and sinks southwards between Puerto Rico and the northern Leeward islands by Friday into the weekend. This in turn will destabilize the upper levels and favor better chance for early morning and afternoon convection across the region over the weekend. Activity however should be more localized and not widespread. However, good daytime heating and local effects will support enhanced afternoon convection in some areas across portions of central interior and west sections of Puerto Rico each afternoon. Lesser activity is so far forecast around the U.S.Virgin islands where mostly isolated showers will be possible for the most part.

The prevailing surface features will be a building surface high pressure over the west and southwest Atlantic, interacting with what is now Tropical Storm Gordon. This is still forecast to move well northeast of the region over the Central Atlantic and have no direct impacts on the islands. Under this expected pattern, a mix of sunshine and clouds and variable weather conditions are forecast, with an overall drier airmass to remain in place, along with some traces of suspended dust particulates. The occasional passage of bands and shallow pockets of moisture from time to time can be expected across the region. This will be sufficient to aid in the development of nocturnal and diurnal convection each day.
This scenario along with the intense daytime heating will lead to periods of enhanced afternoon convection in isolated areas especially across portions of Puerto Rico each day.

For the most part, the winds are expected to be fairly light and therefore any locally and diurnally induced afternoon activity will will be sufficient to produce slow-moving showers and thunderstorm with locally heavy rains. This may lead to periods of elevated flood threat especially across the central and west to southwest sections of Puerto Rico.

AVIATION
(18Z TAFs)

Expect mostly VFR except vcty SHRA/TSRA where mtn obscurations will be likely. Most TAF sites will be unaffected, but TJBQ may have brief interludes of MVFR conds. Sfc winds SE 10-15 kts with sea breeze intrusions along the northwest and west coasts and where they would occur due to the onshore nature of the general flow. Aft 15/22Z land breezes will develop and SHRA activity will greatly diminish. Winds will shift to more easterly before 16/12Z and sea breezes will recommence arnd 16/12Z at 10-15 kts with gusts to 22 kt psbl. Outlook: Conds impvg with much less mstr Monday and Tuesday.

MARINE

A weak surface high pressure, now northeast of the area, will move west across the Atlantic waters about 400 miles north of Puerto Rico Monday night. East southeast winds of 10 to 15 knots will prevail, turning more easterly tonight and Tuesday. Showers will become isolated over the local waters as drier air moves in. A few thunderstorms are possible off of the western coast of Puerto Rico.
Overall seas will range between 2 to 4 feet occasionally up to 5 feet over the offshore Atlantic waters and passages and between 1 to 3 feet elsewhere during the next 5 to 7 days.

BEACH FORECAST

Tonight, beachgoers can expect a low risk of rip currents along most of the local beaches of the USVI and PR. Winds along the coastal areas will be between 10 to 15 mph with sea breeze variations and occasionally higher gusts during the afternoon hours.



SJU WATCHES/WARNINGS/ADVISORIES
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>003-007- 008-010>013.

Excessive Heat Warning until 5 PM AST this afternoon for PRZ005.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.