Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
365 FXCA62 TJSJ 150920 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 520 AM AST Sat Jun 15 2024 .SYNOPSIS... Another warm day is forecast for the northern and northwestern coastal areas today, where heat indices could reach 100 to 112 degrees Fahrenheit. Given these expected conditions, an Excessive Heat Warning is in effect from 10 AM to 6 PM and a Excessive Heat Advisory for the same time-frame for Culebra, Vieques and the U.S. Virgin Islands. Another warm day is forecast for tomorrow where a Excessive heat Watch remain in place for most of the northern coastal area. Please follow the recommendations from the local health department to avoid heat exhaustion. Additionally, convection is expected as plenty of moisture remains in the area, brought in by the southeasterly wind component. && .SHORT TERM...Today through Monday... A surface trough will continue to exit the region today with trailing moisture expected to affect the local islands and coastal waters during the rest of the morning hours, steered by the prevailing southeast low level winds. Recent Doppler weather radar VAD wind profile suggest winds veering southeast-south below 700 millibars favoring a warm moist environment in the low levels. Mid to upper levels suggests the region remains on the subsident side of the trough lingering east of the region, while an upper ridge will hold just to our west. Expect this overall pattern to persist through the weekend with a light to moderate plume of Saharan Dust and suspended particulates expected to continue crossing the region today through Sunday. Although the highest concentration of dust should move just south of the region, the low level wind flow will bring sufficient dust for slightly hazy conditions especially later today and on Sunday. Although drier air will filter in across the region today along with the Saharan dust, there will enough moisture available to aid in the development of afternoon showers and isolated thunderstorms each day. With fairly light winds and local sea breezes, most of the expected rainfall should be focused across eastern, central and northwest sections of Puerto Rico steered by the southeast wind flow. The suspended Saharan dust particulates, along with the warm southerly flow and presence of the mid to upper level ridging will continue to favor subsidence and support above normal daytime high temperatures in the low 90s especially along the north and west coastal areas. That said, maximum heat indices are expected to exceed 100 degrees once again, resulting in excessive heat impacts especially along the west, north and east coastal and urban areas. These conditions will also remain likely on Sunday. Therefore excessive heat warnings and advisories will be issued for portions of the islands today and a Heat Watch will remain possible for Sunday. Please refer to the latest Non-Precipitable Weather Message(NPWSJU) issued by WFO SJU PR for additional information on these heat impacts. .LONG TERM...Tuesday through Saturday... A deteriorating weather trend is forecast for the first part of the long-term period. A trough will build just over the western Atlantic at the upper and mid-levels. The presence of the mid- to upper-level feature will decrease the 250 MB height and turn the temperatures at 500 MB colder, ranging from -7 to -8 degrees. This increases the potential for more widespread lightning activity on Tuesday into Wednesday. According to the global model guidances (GFS and ECMWF), surface conditions will also be favorable for shower activity due to plenty of tropical moisture embedded in the east-southeasterly wind flow across the region. Given the expected conditions from Tuesday into Wednesday, the islands will experience passing showers in the morning hours over the eastern sections, the U.S. Virgin Islands, and the local waters, followed by widespread shower activity across the western interior. So far today, the rainfall threat is mostly concentrated across the western interior, with ponding of water in roadways and poor drainage areas. From Thursday into Saturday, plenty of surface moisture will continue to stream across the local islands, keeping the potential for convection in the afternoon, especially across the mountains and the western interior. Although plenty of moisture will remain in place, more stable conditions will be present at the upper level, provided by an upper-level ridge. A similar temperature pattern is expected across the islands by the first part of the long term. According to the model guidances, 925 MB temperature, the trend calls for warmer conditions, resulting in heat indices rounding 108 to 112 F degrees. Residents and visitors are urged to stay informed of possible advisories or warnings due to Excessive heat. && .AVIATION... (06Z) SFC trough crossing the region will bring wdly SCT SHRA with SCT ocnl BKN cld lyrs nr FL025...FL050..FL080 over regional waters and en route btw islands. VFR conds will prevail at all terminals but Tempo 4-5SM psbl with SHRA at TJSJ/TIST/TISX til at least 15/12Z, Brief MVFR and Mtn top Obscr psbl ovr Eastern PR due to low clds and -SHRA. SFC wnd calm to lgt/vrb but with a light(5-15 KTS) southerly component in the low levels BLO FL100. SFC wnd bcmg mainly fm the SE around 10 kts aft 15/14Z. && .MARINE... A broad surface high pressure over the eastern Atlantic extending into the Central Atlantic interacting with an induced surface trough just north of the CWA will continue to promote a light to moderate south-southeasterly. Under this pattern and tropical islands, the local waters will experiment with seas up to 5 feet and winds up to 15 knots. Isolated to moderate showers with thunderstorm activity would result in localized hazardous marine conditions. There is a low risk of rip currents for all the exposed coastal beaches in the region. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Excessive Heat Warning from 10 AM this morning to 6 PM AST this evening for PRZ001-005-008-010. Excessive Heat Watch from Sunday morning through Sunday afternoon for PRZ001-002-005-008-010-012-013. Heat Advisory from 10 AM this morning to 6 PM AST this evening for PRZ002-012-013. VI...Excessive Heat Watch from Sunday morning through Sunday afternoon for VIZ001-002. Heat Advisory from 10 AM this morning to 6 PM AST this evening for VIZ001-002. AM...None. && $$ SHORT TERM...RAM LONG TERM....LIS AVIATION...RAM