####018002200#### FXZS60 NSTU 040122 AFDPPG Area Forecast Discussion National Weather Service Pago Pago AS 222 PM SST Fri May 3 2024 .Short term... As of this morning and early afternoon, satellite imagery shows most of the rainfall that would cause flash flooding has remained to the north and east of American Samoa. Therefore, the Flood Watch expired this morning. However, the atmosphere over the territory is unstable with above average moisture along the lower and middle levels. This will continue to create on and off showers with a slight chance of thunderstorms through the overnight hours and Saturday. Winds will remain from the northeast up to 15 mph, but may have stronger wind gusts in periods of rainfall. By Saturday evening and Sunday, a low pressure system will develop within the trough and move southward to squeeze between two high pressure systems to the southeast and southwest. This may create enough moisture and instability to produce flash flooding over American Samoa during this time. We will continue to monitor this timeframe and will likely issue a Flood Watch if the forecasted weather pattern continues to hold. Winds are forecast to become northerly, but remaining up to 15 mph with the exception of near localized thunderstorms. .Long term... The aforementioned weather pattern of above average rainfall is forecast to continue through Monday. Easterly flow would reduce the rainfall to scattered showers by midweek. However, we will track the placement of a high pressure system well to the southwest as it may push a trough over the region again during this time through the end of the week. && .Marine... The latest information from the altimetry data of a recent POES satellite pass over shows seas around 8 feet throughout the coastal waters region. Winds continue to decrease as it becomes northeasterly, but gusty winds may occur in localized thunderstorms and waves will remain choppy through the weekend and into early next week. && .PPG WATCHES/WARNINGS/ADVISORIES... A Small Craft Advisory remains in effect. && $$ LaPlante ####018005848#### FXHW60 PHFO 040125 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 325 PM HST Fri May 3 2024 .SYNOPSIS... Breezy trades will become slightly more unstable with pockets of heavier showers possible through the weekend, mainly windward and mauka. A drier moderate trade wind pattern then becomes established by the middle of next week. && .DISCUSSION... Regional satellite shows a closed upper low positioned just SE of 170N/30N. Modest convection, including a few thunderstorms, are noted within its core and beneath the cold pool aloft (-15C at 500mb) several hundred miles NW of the Hawaiian Islands. A shortwave trough wrapping around the southeast periphery of this low enhanced trade wind showers last night and is now lifting north of the area. As a consequence, showers have decreased in coverage during the last several hours. Otherwise, trade winds have settled in and will take the edge off of afternoon heat compared the last several days as showers focus over windward and mauka zones in routine fashion. Trades will then acquire a decreasingly stable character as the aforementioned upper low opens up and shears east along the northern periphery of the subtropical jet. The inversion is modeled to weaken and lift by a few thousand feet which will increase the depth of trade wind showers as they advance across the area. This will facilitate slightly greater rain rates and increase leeward penetration of showers. Waves of forcing rotating around the low will be responsible for periodically increasing shower coverage Saturday night through early next week. During this time, the cold pool aloft will move directly overhead and is modeled to moderate to around -11C at 500mb. Lapse rates will still be adequate for pockets of deep convection to develop Sunday night through Monday night, mainly during the overnight periods. Isolated thunderstorms cannot be ruled out during this period, but confidence at this stage is too low to warrant explicit inclusion in the forecast. Meanwhile, a separate thunderstorm threat may manifest over the Big Island where a plume of steep lapse rates on the order of 7C/km is modeled to extend northeastward over the eastern end of the state. This will contribute to an increased probability of pockets of heavy showers and/or isolated thunderstorms Sunday and Monday afternoon, particularly as the upper jet provides maximum venting aloft on Sunday followed by the upper wave itself pivoting through on Monday. Confidence at this stage once again falls short of inclusion in the forecast but will be given consideration in future forecast cycles. Pressure falls over a broad swath of the Central Pacific will then ease the gradient leading to a drier moderate trade wind pattern by the middle of next week. && .AVIATION... Breezy easterly trades will continue through the weekend as high pressure builds in from the NE. Moisture riding in on the trades will focus clouds and showers over windward and mauka areas, with the greatest shower activity during the late night and early morning hours. A few showers may spill over to leeward areas at times. VFR conditions will generally prevail, but MVFR conditions will be possible in any heavier showers that develop. AIRMET Sierra is in effect for tempo mountain obscuration for windward and mauka portions of the island chain. This AIRMET will likely be needed through tomorrow morning. AIRMET Tango is in effect for mod turb below 9000 feet downwind of island terrain. Conditions are borderline, but should continue through Saturday. AMD NOT SKED in for Midway due to missing wind speed and direction && .MARINE... High pressure far north-northeast of the state will produce fresh to strong trade winds across Hawaiian waters for the next several days. These stronger trades may ease slightly early next week as the high begins to move farther to the northeast. An advanced scatterometer (ASCAT) pass today continued to show Small Craft Advisory (SCA) level winds across most coastal water zones, a trend which will continue through the weekend. As a result, a SCA remains in effect for all Hawaiian waters through early Monday morning. Surf along north and west facing shores remains tiny this afternoon, but a small, long-period northwest swell will fill in this evening and tonight, peak on Saturday, then gradually decline into Sunday. Observations from Buoy One (51001) suggest that forerunners from this swell should begin arriving at Kauai late this afternoon, followed by Oahu this evening, and finally Maui and the Big Island during the overnight through early morning hours. This swell will increase surf heights noticeably for north and west facing shores tonight through Saturday, but will remain in the small category. Another small, long period northwest swell will fill in late Sunday, maintaining small surf along north and west facing shores into early next week. Small background south swells will continue into Saturday, providing tiny surf for south facing shores. Forerunners of a small, long period south swell may arrive Saturday afternoon with a slow onset through Sunday providing a boost in surf along south facing shores into early next week. Rough and choppy surf along east facing shores will increase slightly on Saturday and hold into early next week as strong trades persist. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Monday for all Hawaiian waters- && $$ DISCUSSION...JVC AVIATION...Farris MARINE...Vaughan