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| Temp |  | -1.1 C |
| RH | | 23 % |
| Wind | | S 15 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 973 FXHW60 PHFO 031337 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 337 AM HST Fri Apr 3 2020 .SYNOPSIS... An area of low pressure northwest of the state and a ridge of high pressure to the east will keep a light wind regime in place across the islands through early next week. Showers will favor areas near the coast at night and the interior of the islands during the afternoon and evening hours. Some deeper moisture will get drawn northward Saturday night through early next week, bringing the potential for some locally heavy downpours and a few thunderstorms, mainly during the afternoon and evening hours. The light wind regime featuring mainly afternoon and evening showers looks to hold in place through the middle to latter part of next week. && .DISCUSSION... Currently at the surface, a trough of low pressure is located around 150 miles west-northwest of Kauai. Further displaced from the islands, a 1010 mb low is located around 1050 miles northwest of Kauai, with a 1029 mb high around 1600 miles northeast of Honolulu. The resulting gradient is producing light to moderate east to southeast winds from Oahu to the Big Island, strongest on the eastern end of the island chain. Meanwhile, a light and variable flow has set up around Kauai and some of the more sheltered locations on Oahu and Maui County, where land breezes are in place. Infrared satellite imagery shows partly cloudy skies in most areas, with a bit more cloud cover over portions of Kauai. Additionally, some scattered to broken jet stream cirrus is streaming overhead. Radar imagery shows scattered showers moving through Kauai in the southerly boundary layer flow, with mainly rain free conditions elsewhere. Main short term concerns revolve around rain chances the next several days. The surface trough just northwest of the islands will gradually dissipate today. Meanwhile the low far northwest of the state will shift southward and closer to the islands, while the high northeast of the area gradually weakens. This will result in the low level boundary layer flow shifting more southeasterly across the island chain, sheltering the smaller islands sufficiently to allow for daytime sea breezes. Moderate southeasterly winds will hold in place across the Big Island however. A few showers will continue to move onshore across Kauai this morning, while the other islands remain generally rain free. With daytime heating we should see some showers develop over the interior of the all islands this afternoon, with an isolated thunderstorm possible over the Big Island slopes. Tonight through Tuesday, model solutions are in generally good agreement showing a relatively stationary low wobbling around well north-northwest of the state, with a ridge of high pressure well to the northeast. This is expected to keep a fairly persistent south to southeast boundary layer flow in place across the island chain, with daytime sea breezes and overnight land breezes dominant across the smaller islands while light to moderate southeasterly winds prevail around the Big Island. The pattern will not change much tonight and Saturday, with lingering showers ending in the evening in most areas. A few showers may continue to roll onshore into Kauai and Oahu through the night and morning hours Saturday, and a few showers may also affect windward portions of east Maui and east and southeast facing sections of the Big Island. Another round of daytime heating driven showers can then be expected over the island interiors Saturday afternoon, and a thunderstorm or two could even develop over the Big Island slopes. A tap into some deeper moisture will begin to lift northward over the islands beginning Saturday night with precipitable water values climbing into the 1.5 to 1.7 inch range. This deeper moisture will then linger over the islands in a broad convergent south to southeasterly flow through Tuesday. The latest guidance continues to support the potential for some locally heavy downpours, particularly during the afternoon and early evening hours each day, with showers most likely in areas near the coast at night. A few thunderstorms can't be ruled out during this period either, mainly over the island interiors during the afternoon/early evening hours and over the coast waters at night. Wednesday through next Thursday, the gradient appears to weaken even further, with daytime sea breezes and overnight land breezes dominant across the entire island chain. Model solutions differ on how much lingering deep moisture will remain over the islands, but it does appear that slightly more stable that over the weekend and early next week. As a result, we expect showers to continue to be driven by daytime heating over the island interiors during the day, and showers hugging the coasts at night. && .AVIATION... A low pressure system approaching the islands from the northwest will keep light and variable winds in the forecast through the weekend. Expect land and sea breezes over each island with wind directions becoming more variable than normal as southerly flow moves over the western islands. Clouds and a few showers will build up over island interior sections this afternoon. Isolated thunderstorms remain in the afternoon forecast for the Big Island. More unsettled weather will move up from the south over the next 24 hours, increasing cloud and shower trends from Saturday to Sunday. AIRMET Sierra in effect for Tempo Mountain Obscuration for Kauai. This AIRMET will likely continue through the morning hours. && .MARINE... A front slowly approaching the region from the northwest will cause the surface ridge far north of the area to weaken. This will cause the winds to weaken and veer slightly more out of the south over the western waters. However, the southeasterly winds over some of the waters across the eastern end of the island chain will strengthen slightly today. There is a chance the southeast winds may be near the Small Craft Advisory criteria over the Big Island Windward and Southeast Waters. From later this weekend into early next week, a broad area of south to southeasterly convergent flow will set up over the state. This will likely bring unsettled weather with locally heavy rainfall and thunderstorms possible from Saturday into early next week. A new north-northwest swell spreading across the area Saturday will produce moderate surf along most north and west shores over the weekend, but surf heights are expected to remain below the High Surf Advisory (HSA) criteria. As the weekend swell subsides, a new west-northwest swell will spread across the area Sunday night, and peak Monday. A reinforcing northwest swell arriving late Tuesday night will likely cause another boost to surf heights along most north and west facing shores Wednesday and Thursday. Southeast swells originating in the South Pacific are being partially blocked by the islands of French Polynesia. However, our current southeast swell appears to be passing through a narrow swell window. This swell will continue to drop through tonight. A small south-southeast swell is possible early next week. Surf along east shores will slowly subside as the trade winds weaken. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Jelsema AVIATION...Bohlin MARINE...Houston Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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