textproduct: San Juan

KEY MESSAGES

* Saharan dust will persist across the region through at least early Monday.

* A tropical wave will approach the area by tomorrow.

* The rip current risk will become low from tomorrow onwards.

LONG TERM...Sunday through Thursday.

A relatively variable weather pattern is forecast across the region from Sunday through Thursday, influenced by several upper- level features, surface patterns, and an intrusion of Saharan dust by the beginning of the period. On Sunday, there will be a slight presence of instability aloft due to a cut-off low located over Hispaniola that might result in moisture advection across the area. Meanwhile, at the mid-levels (500700 MB), a ridge will help maintain a relatively stable environment aloft. At the same time, a plume of Saharan dust is expected to move over the region, with concentrations capable of reducing visibility between 0.20 and 0.30 inches, resulting in hazy skies and possible air quality deterioration. Overall, Sunday appears to be a quiet day with hazy skies and limited shower development. However, daytime heating and the local mountains will lead to the development of afternoon convection, particularly in the interior and western parts of Puerto Rico. Similar activity will be possible for the U.S. Virgin Islands in isolated areas, mostly in the evening hours.

By Monday, another cut-off low will migrate from the northeast into the northern portion of the region, further increasing moisture levels and cloudiness. This upper-level feature will enhance patches of cloudiness and moisture, which will be transported westward by the prevailing easterly trade winds. The interaction between this feature, surface heating, and local effects will result in scattered showers and isolated afternoon thunderstorms, mainly over the interior and western sections of Puerto Rico each day. Trade winds will persist from the east under the influence of a broad surface high pressure system stall over the central Atlantic. On Thursday, the pattern will remain similar, with southeast winds gradually taking hold as a broad surface high over the central Atlantic extends further into the Caribbean. Days will remain variable, with occasional passing showers in the trade wind flow during the morning and overnight hours, followed by pockets of afternoon convection over interior and western Puerto Rico. So far today, although model had some high level of uncertainty, Wednesday into Thursday will be the most unstable days for the long term period.

AVIATION

(18Z TAFS)

VFR conditions across most TAF sites. SHRA/TSRA will continue across interior and northwestern PR through 03/20Z, with brief periods of low ceilings and reduced VIS possible at TJBQ. Showers will diminish after 03/23Z. E-SE winds around 5-8 kts after will prevail after 23Z, increasing after 04/13Z to around 10-15 kts, with stronger gusts near the heaviest shower activity.

MARINE

A broad surface high pressure over the central Atlantic will continue to result in moderate to fresh easterly winds across the region. Therefore, wind-driven seas will result in choppy marine conditions across the Atlantic waters and the Caribbean Waters. Saharan dust particles will be in place, resulting in hazy skies and limited shower activity until Friday, when another tropical wave moves into the islands, bringing showers and thunderstorms.

BEACH FORECAST

The rip current risk will become low by Friday and will remain like it through the weekend.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>005-007- 008-010-011.

VI...None. AM...None.