| Current Conditions | ||
| Temp |  | -1.9 C |
| RH | | 9 % |
| Wind | | SW 31 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 732 FXHW60 PHFO 241342 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 342 AM HST Mon Feb 24 2020 .SYNOPSIS... Light and variable winds in the morning will transition into moderate trade winds later this afternoon as high pressure builds back in north of the Hawaiian Islands. Trade winds will increase through the week, becoming breezy on Tuesday, and Windy from Friday on through the weekend. Clouds and scattered showers will favor windward and mountain areas through Wednesday, then trend towards a wet trade wind pattern with numerous showers developing as an upper level disturbance moves into the eastern half of the state from Thursday through Sunday. Long range forecast guidance suggests wet trades may linger into the first half of next week. && .DISCUSSION... A rapidly weakening cold front has stalled just north of the islands this morning as a migratory high center builds in north of the state. Light and variable winds will continue through the morning hours as we transition to moderate trade winds later this afternoon. A slight increase in cloud cover and shower activity will develop due to convergent trade winds flow under the influence of a weak upper level trough. Breezy trade winds are expected from Tuesday through Thursday with gusts around 30 MPH in some wind favored locations. Rain shower activity will follow a more normal trade wind pattern with isolated to scattered showers along windward and mountain areas with drier more isolated activity through Wednesday. On Thursday the weather changes towards a wetter and windier pattern lasting through the weekend. A stronger high will build in far north of the islands as a fairly strong upper level trough deepens and moves into our area from the north. This upper trough will destabilize the region by lifting the trade wind inversion heights allowing for deeper cumulus clouds to form across the state. These more unstable cumulus clouds will be caught up in the strengthening trade winds and pushed up over the mountain ranges of each island resulting in an extended period of wet weather for all islands. Windward areas will see the highest rainfall amounts, however even leeward slopes will see periods of shower activity in these unstable conditions. On Friday, an upper level cold core low forms at the base of this upper trough and settles in just east of the island chain. Cold temperatures and dynamic forcing aloft will continue to destabilize trade wind clouds upstream of each island through Sunday. Global weather models remain in good agreement with this blasting wet trade pattern, and our confidence levels are good for this next wet weather event. Rainfall amounts remain highly dependent upon the strength and location of this upper level cut off low as it meanders towards the Hawaiian Islands this weekend. Higher rainfall amounts will tend to favor the eastern Hawaiian Islands due to their closer proximity to the upper low. Snowfall on the highest peaks of the Big Island are possible with several inches of snow forecast over Mauna Kea and Mauna Loa by the end of this weekend. Meanwhile windy trades remain in the forecast as high pressure continues to build in north of the state from Friday through Sunday. Surface wind speeds will likely exceed wind advisory thresholds and approach high wind warning conditions for the low elevation sites. The highest mountain peaks on the Big Island will reach wind advisory conditions and possibly exceed high wind warning thresholds. A High Wind Watch may be required for the wind favored areas of the Hawaiian Islands including the slopes of Mauna Kea and Mauna Loa from Friday through Sunday. Extended forecast guidance for early next week suggests the upper level low will drift westward over the Hawaiian Islands potentially keeping wet weather trade winds in the forecast for a few more days. Stay tuned. && .AVIATION... Light northerly winds will allow the land breezes to hold through the early morning hours today for most areas, before moderate to breezy trades quickly fill in through the afternoon hours. There may be a small window of time for a few hours of sea breeze conditions around and by noon before the trades become established. Brief periods with MVFR CIGS/VSBYS will remain possible as showers develop and move ashore within the light northerly flow this morning, mostly for northern facing slopes and coasts. As the trades return, the cloud/shower coverage will transition back to the typical windward areas. AIRMET Tango is in effect across the entire state for tempo moderate turbulence between FL200 and FL250. This AIRMET will likely be dropped later this morning. && .MARINE... A stalled front will slowly dissipate northwest of Kauai today, as high pressure builds eastward along 30N. Light trade winds will prevail this morning, with the trades then ramping up to moderate and fresh levels during the afternoon. High pressure will continue to build northeast and strengthen tonight through next weekend, resulting in gradually strengthening trade winds. SCA level winds will likely develop around the typically windy areas around Maui County and the Big Island beginning tonight. Winds are expected to strengthen further through the week, so the SCA will likely expand to additional marine zones through the week. Most marine zones will experience SCA conditions by the weekend, with Gales possible across some of the typically windy areas. The current northwest swell will gradually lower today. A large northwest swell is expected to arrive tonight, peak late Tuesday and Tuesday night well above advisory levels, and could potentially reach marginal warning levels along north and west facing shores at the peak. The swell will then gradually subside Wednesday through Thursday, with a new large northwest swell arriving late Wednesday night into early Thursday. This new swell will peak Thursday night and Friday, with surf likely reaching advisory levels, then gradually decrease through the weekend. Surf along the east facing shores will gradually trend up through the week as the trades increase, and will likely reach advisory levels next weekend. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Bohlin AVIATION...Gibbs MARINE...Jelsema Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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