Current Conditions | ||
Temp | ![]() | -0.2 C |
RH | ![]() | 100 % |
Wind | ![]() | SW 57 mph |
Road | ![]() | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 599 FXHW60 PHFO 221350 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 350 AM HST Fri Feb 22 2019 .SYNOPSIS... A surface trough near the Big Island will support clouds and showers over the eastern end of the island chain into Saturday. Meanwhile, weak high pressure to the northwest will support mostly dry weather over Kauai and Oahu. Light winds will continue today, but a new high building northwest of the islands late Saturday will bring gradually strengthening north to northeast winds on Sunday that may become breezy next week. These winds will deliver clouds and showers to north and east facing slopes and coasts, while also bringing cooler air to the islands. && .DISCUSSION... Currently, a persistent N-S oriented surface trough just E of the Big Island is fueling clouds and showers near its axis, while a weak bubble high to the NW of the islands is supplying mostly dry weather and light winds to most of the state. SW flow just above the surface is supplying broken to overcast layered clouds (based near 8000 feet) to parts of Maui county and all of the Big Island, with nearly clear skies over Kauai and Oahu. A few thunderstorms have been observed overnight over the Hawaiian Offshore waters about 50-70 miles SE of the Big Island. The surface trough will drift W today, remain nearly stationary into Saturday, and then move away to the E by Sunday. Clouds and showers will be maximized near the trough axis, primarily affecting windward and SE Big Island, but potentially spreading to portions of Maui. Elsewhere, a mostly dry light wind regime will continue into the weekend. Light winds today will allow afternoon sea breezes to drive cloud formation over interior portions of Kauai, Oahu and parts of Maui county, with little rainfall expected. On the Big Island, the layered cloud cover is likely to remain thick enough to preclude daytime heating from prompting shower formation over the slopes, and instead the approaching surface trough will do so. With PWAT near 2" near the trough axis, some locally heavy downpours will be possible, with showers expected to primarily affect the E half of the Big Island. As a shortwave approaching from the NW moves over the area this afternoon and tonight, showers along the trough axis may become enhanced. A slight chance of thunderstorms has been added to the forecast for the Big Island and portions of the adjacent waters. Over the weekend, the surface trough will weaken and shift E as a new high builds NW of the islands. This high will bring light to moderate N to NE winds that will push the remnants of a cold front over the islands from the N, and bring a cooler air mass. This moisture will likely fuel a few showers along N and E facing slopes and coasts from late Saturday into Monday. A stronger high is expected to develop NW of the islands Tuesday and Wednesday, likely leading to locally breezy N to NE winds that will usher additional frontal moisture over the islands as low pressure develops (once again!) NE of the islands. This development would keep NW to N winds over the islands toward the end of the week, delivering passing clouds and showers. && .AVIATION... Patches of mid-level clouds continue to stream across the eastern end of the island chain early this morning. The background low- level flow will remain light today as a weak surface trough near the eastern Big Island tracks slowly westward. An area of enhanced moisture also remains in the vicinity of the Big Island. This is expected to cause low clouds and showers to increase over the windward Big Island this morning. AIRMET Sierra for mountain obscuration due to these low clouds and showers is in effect for the windward Big Island. By this afternoon, a slight chance of thunderstorms is also included in the forecast for most of the Big Island. The low clouds and showers are expected to spread over portions of windward Maui later today and tonight. As a result, AIRMET Sierra may need to be extended to windward Maui. Elsewhere, mainly VFR conditions are expected to prevail today. && .MARINE... Light northeast winds will continue across most Hawaiian waters into the upcoming weekend, then shift out of the north and increase into the light to moderate category late Saturday through Sunday. Near the coasts, overnight and early morning land breezes followed by late morning and afternoon sea breezes will continue through Saturday. The increase out of the north to northeast direction late Saturday through Sunday may be strong enough to hold off the sea breezes from developing Sunday. The exception will be around the Big Island due to a trough of low pressure that is forecast to linger in the area into the weekend. Moderate to fresh breezes (northeast winds west of the trough and southeast winds to its east) will hold across the windward and southeast Big Island waters today. The trough will begin to shift east over the weekend as high pressure builds to the northwest and a front passes to the north. Despite the light winds in place, seas are slow to lower due to the large easterly swell that has been in place. This swell has peaked and will continue to lower through the weekend. Surf along east facing shores will respond and gradually ease into the weekend. After a long stretch of large surf and northerly winds for our north facing shores through the first half of February, surf will near a minimum for the month through the weekend. Storms over the far northwest Pacific have been quickly lifting north-northeast from Japan to the Bering Sea, ultimately limiting our traditional setup for northwest swell sources. A cold front will approach and move into the area from the north Monday night through midweek, which will bring fresh to strong north winds and rough seas (small craft advisory conditions) across the waters Tuesday through midweek. Surf along north and west facing shores is expected to rise next week in response to a powerful hurricane-force low projected to develop off the coast of Japan Saturday, then race northeastward toward the Aleutians/Date line Sunday. WAVEWATCH III and the ECMWF- Wave solutions depict a large long-period northwest (320 deg) swell evolving from this source moving through the Hawaiian waters Tuesday through midweek. If this materializes, surf could near warning levels for exposed north and west facing shores Wednesday through Thursday. && .HFO WATCHES/WARNINGS/ADVISORIES... Wind Advisory until 6 PM HST this evening for Big Island Summits. && $$ DISCUSSION...Birchard AVIATION...Houston MARINE...Gibbs Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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