444 FXCA62 TJSJ 111423 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 1023 AM AST Thu Oct 11 2018 .UPDATE... Partly cloudy conditions are prevailing across Puerto Rico with isolated showers over eastern areas of Puerto Rico. A TUTT low as begun to develop to the northwest of Puerto Rico, and will hold through the weekend. A tropical wave in the Western Caribbean will interact with a mid to upper level low, and transport a plume of moisture over northwestern Puerto Rico and local waters. Therefore as a result of increased moisture and instability due to TUTT low, showers and thunderstorms are forecast to develop across the northern areas of Puerto Rico early this afternoon, then over the interior and western areas later this afternoon. && .AVIATION... VFR/MVFR conds are expected today across most terminal sites as a result of SHRA/VCTS. SHRA are forecast to develop across TJSJ and points east by 11/14 and then across TJBQ and TJMZ by 11/15Z. VSBY's could fall to MVRF due to +RA and TSRA later this afternoon, then showers should diminish by 11/23Z. Ea at 8 to 15 kts with higher gust within TSRA. Winds will be from the east to northeast at 10 to 15 kts with sea breeze variations past 11/15Z. && .MARINE... Seas will range from 4 to 6 feet across all outer and local water ways. Therefore, small craft operators should exercise caution today. High risk of rip currents continues in effect for the northern beaches of PR as well as Cramer Park in Saint Croix. && .PREV DISCUSSION... /issued 449 AM AST Thu Oct 11 2018/ SYNOPSIS...Upper-level trough will become situated near the region during the next several days and will combine with a deep plume of tropical moisture to result in an unsettled weather pattern through early next week. Improving weather conditions expected by the latter half of next week as a drier airmass moves in from the east. SHORT TERM...Today through Saturday... The available moisture will gradually increase from the south as the day progresses. There is also an upper trough that is developing to the west of the local area as it erodes the upper ridge. The upper trough will continue developing for the next few days, which will gradually dig to the west of the local area. The moisture advection expected today will combine with the local effects, diurnal heating and the improving upper level divergence to cause the development of showers and thunderstorms this afternoon across many sectors of Puerto Rico, especially western PR and the eastern third of the island. Elsewhere, scattered showers with isolated thunderstorms are expected. Even though the upper trough is expected to be in a much more favorable position by Friday, the high resolution models, particularly the WRF is rather bullish with the amount of rainfall and thunderstorm potential today. The increase in moisture will continue on Friday and for the next several days after that, with precipitable water values near 2 inches. However, the high resolution models are insisting that Friday will not have as much rainfall as today, this could be given to the layer of cloudiness that is expected, which may limit convection to a few areas, likely to the northern and northwestern sections of PR, with shower and thunderstorm activity increasing late in the afternoon and into the evening as the upper trough positions itself in a better location to produce favorable dynamics for thunderstorm development over the local area into Saturday. This means that Saturday could be a day with numerous showers and scattered thunderstorms. At this time there is very little to suggest the contrary. The upper trough will be in a good location, there will be plenty of moisture, and there will be divergence in the upper levels. At this time, it looks like Late Friday into Saturday could be have numerous showers and some thunderstorms from late Friday into Saturday. No change in the temperatures is expected for today, with the max temps in the mid to upper 80s across the lower elevations and in the low 80s across the higher elevations. LONG TERM...Sunday through Friday... Upper-level trough will continue to be situated near the local area through early next week, providing favorable upper-level dynamics and decent instability aloft. This trough in combination with the deep plume of tropical moisture expected to envelop the region through the southeasterly wind flow will create a favorable environment for the development of shower and thunderstorm activity across the forecast area through at least Tuesday. However, a caveat for the potential for heavy rainfall each day throughout the period is the amount of mid to upper-level cloudiness that could potentially be present. If there is enough cloudiness to limit diurnal heating and therefore the instability, then rainfall activity could be limited across the region each day. This is something that will have to be monitored during the next several days. Nevertheless, if the heavy rainfall does indeed materialize then there will be an increased potential for urban and small stream flooding as well as mudslides in areas of steep terrain. A drier weather pattern is expected during the latter half of next week as a drier airmass is forecast to move in from the east, which will aid in decreasing the moisture content, therefore limiting the shower activity across the forecast area. AVIATION...Sct SHRA expected across the local area through 11/14Z, causing VCSH at TIST and TISX. However, VFR conds expected across the local terminals through 11/16Z, with SHRA/TSRA developing and likely affecting the terminals or the vicinity of the terminals in PR thereafter. Winds will be from the east to ENE at 10 to 15KT and gusty with sea breeze variations past 11/14Z. Winds may be slightly stronger near thunderstorms. MARINE...Choppy seas between 4 to 6 feet will continue to prevail mainly across the Atlantic waters, Anegada Passage, and the offshore Caribbean waters. Therefore, small craft operators should exercise caution across these waters. Across the rest of the regional waters, seas between 2 and 5 feet will prevail. East winds between 10 to 15 knots will also prevail. High risk of rip currents continues in effect for the northern beaches of PR as well as Cramer Park in Saint Croix. && .PRELIMINARY POINT TEMPS/POPS... SJU 87 78 89 77 / 60 50 50 70 STT 89 78 89 76 / 50 40 50 70 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through late Friday night for North Central-Northeast-Northwest-San Juan and Vicinity-Southeast- Western Interior. VI...High Rip Current Risk through late Friday night for St Croix. AM...None. && $$ SHORT TERM...99 LONG TERM....99