Showers and thunderstorms will continue into tonight, mainly over western islands. Light southeast surface winds will give way to increasing trade winds late Saturday through into Monday. A new area of increased moisture will move in Monday/Tuesday, with mainly windward showers. Southeast winds are likely to return late next week, but without as much moisture as our current southeast flow situation.
Showers with isolated thunderstorms have covered parts of the state today, including a strongly rotating storm over Niihau early this morning. This storm was strengthen in part by strong wind shear and an interaction with an outflow boundary from previous convection. The rotation was strong enough to have produced a tornado, but due to the location of the event, we will likely never know if one actually occurred. Heavy rain was reported in several locations, including central Oahu, and flood advisories were in effect for Kauai and Oahu earlier today. Showers have moved mostly offshore as of 2 PM HST.
Additional showers and thunderstorms are in the forecast for tonight into early Saturday, and short range ensembles showing the main risk will remain over western islands. With light low- level winds, the enhanced moisture that has impacted the state this week will still be with us tonight and into Saturday. PW values range from roughly 1.5 to 1.8 inches. Therefore, episodes of brief moderate to heavy rainfall remain possible.
An important change in the weather is nearly here. After light southeast winds tonight into early Saturday, trades will move back late Saturday. They will become stronger out of the east Sunday, and even stronger from just north of east Monday. A new area of enhanced moisture will move in from the ENE around this time, enhancing windward showers into early Tuesday.
Trades are forecast to last through Wednesday night, with indications of a possible return to southeast flow late Thursday into Friday.
Widespread light to moderate showers with embedded heavier convective elements are bringing MVFR to localized IFR conditions to Oahu this afternoon. Ample moisture remains in place through tonight as gentle offshore land breezes take hold over most areas. Even with the land breezes, stout SW flow aloft will likely carry pockets of moderate to locally heavy rain over leeward areas at times.
Light winds then give way to afternoon sea breezes on Saturday yielding the potential for convection over island interiors. Trades return late Saturday evening.
AIRMET Sierra for mountain obscuration remains in effect for Oahu.
Scattered to numerous showers and isolated thunderstorms will continue over the western coastal waters tonight. While gusty winds can be expected around any thunderstorms, generally gentle to locally moderate southerly winds will continue, with light and variable winds to the far northwest. By late this weekend, easterly trade winds will gradually build from east to west with the potential for SCA conditions over the windier waters and channels around Maui County and the Big Island. Expect trades to strengthen further early next week as surface high pressure builds to the north.
The current moderate, medium period, north northwesterly swell (340-350 deg) peaked yesterday evening and has been slowly fading since. This north northwest swell will remain elevated through this evening and keep surf just shy of advisory levels through early Saturday along north facing shores. A small to moderate, medium period, northerly swell is progged to fill in late Saturday, along with a small, long to medium period west northwesterly swell. This combination of swells may boost surf heights back up Saturday night into Sunday, but should remain shy of High Surf Advisory criteria. Sunday night into early next week, the swell fades and should allow surf to drop to below seasonal averages.
Surf along east facing shores will remain small given the lack of trade winds upstream of the islands through Saturday, but areas exposed to the north swell will see an uptick through the rest of the weekend. As trade winds gradually strengthen later this weekend, east facing shores could become rough and choppy Sunday through early next week. Surf along south facing shores will remain flat to tiny through the weekend into early next week.
None.
