Last Updated on Friday, 29 August 2014 10:11
Winds Statewide in a glance ...go HERE (this link is also the 4th drop down under weather)
Aug 29, 2014 4:00 AM HST
Easterly swell is still forecast to build over the Hawaiian coastal waters today, and advisory-level surf also will affect south-facing shores. Interaction between the long-period east and south swells may produce strong currents in some areas. The surf from both swells will decline slowly through the weekend.
With trade wind speeds more likely to diminish than to increase through the first half of the forecast period, it is doubtful that they will approach the criterion for a small craft advisory. However, the long-period easterly and southerly swell could produce locally large and confused seas.
High surf advisory until 6 am HST Saturday for Niihau, Kauai windward, Kauai leeward, Oahu south shore, Waianae coast, Oahu Koolau, olomana, Molokai, Lanai makai, Kahoolawe, Maui windward west, Maui leeward west, Maui central valley, windward Haleakala, leeward Haleakala, Kona, south Big Island, Big Island north and east.
The trade winds will weaken further, becoming light by early next week. A trough moving over the southeast half of the state may increase clouds and showers through about noon today. Over the weekend, sea breezes will encourage cloud buildups and a few showers in island interiors by day, while land breezes bring clearing at night. The trade winds may start to return by the middle of next week, though they will remain on the light side of average for some time.
Surface observations around the main Hawaiian islands reported very light trade winds. Precipitation across the state remained sparse, with individual totals also diminishing through the night. Since the inversion stayed high, and precipitable water adequate, these dry conditions probably were supported at least in part by land breezes.
Although a mid-level ridge prevailed to the southeast of the islands, a broad trough was present to the northwest through northeast. Most likely it was this feature that encouraged active towering cumuli to develop near 30°N.
Satellite estimates showed a plume of moister air approaching Maui county from the east, and the cloud feature associated with this plume developed considerably during the past few hours. In-station analysis suggested that this feature remained a trough rather than a closed low, at least near the surface, but in any case it may enhance rainfall later today as it moves ashore over Maui and Hawaii counties. Pops and associated fields have been increased accordingly.
Guidance predicted additional moisture surges to reach the state periodically into next week, though with time the different solutions ended up following different periods, complicating a deterministic forecast. With trade winds very weak by Monday, diurnal showers produced by sea breezes may dominate weather from day to day, with the moisture surges only amplifying the magnitude of the daily event.
In any case, ridging aloft will expand over the islands from the southeast during the weekend, so by next week subsidence will start to crush down the inversion. However, a front north of 30°N will keep the surface ridge anchored near the islands well into next week, so the trade winds will recover only very slowly.