An increase of moisture from the remnants of Norbert will bring a wet trade wind pattern from late Wednesday through Friday. Deep tropical moisture combined with some instability will bring an increase of heavy rain especially over windward and mauka areas. In areas that see less rainfall such as leeward areas, hot and muggy conditions are expected by the middle of the week. Improving weather conditions are generally expected over next weekend, but some scattered showers will likely persist.
This morning's satellite imagery shows a band of moisture east of the Big Island, which will be moving east to west across the state today. 12Z soundings from Lihue and Hilo show a stable trade wind inversion at around 5000 to 6500 ft. While stable conditions are expected to persist over the next few days, the increase of moisture will bring an increase of humidity and some light to moderate showers over windward and mountain areas. Dewpoints are expected to get into the 70s by late Monday into Tuesday, which will bring some muggy weather across the state.
Starting Wednesday and continuing through Friday, the weather pattern will change as the remnants of Norbert moves east to west across the state. Deep tropical moisture from Norbert combined with a weak upper level trough will bring an increase of heavy showers especially by Thursday. With trades picking up to moderate to breezy speeds by late Wednesday into Thursday, the focus of the heavy rain will be over windward and mauka areas. A Flood Watch may be warranted especially for Thursday into Thursday night, but we will wait to see what the high res models show as we get closer to the second half of the week. So overall we are expecting a wet, trade wind pattern during the second half of the week with the focus of the heavier showers over windward and mauka areas. While leeward areas should see some frequent showers, in areas with less shower activity can expect hot and muggy weather, with dewpoints getting up into the mid 70s.
Over the weekend, while the bulk of the deep tropical moisture should move west of the state, showery weather could linger through at least parts of Saturday. But generally improving weather conditions are expected this weekend with moderate to breezy trade winds.
A few light showers have developed tonight, and are drifting over the islands tonight from Kaua'i to Maui, with MVFR conditions possible in showers. Showers should be short-lived, with no significant mountain obscuration expected at this time, however will need to The forecast remains on track with drier trade winds for the Hawaiian Islands tonight into tomorrow. Expecting shower activity to remain limited through tomorrow thanks to these winds, with the windward side of the islands having a 15-40% chance for showers while the rest of the areas remain dry. Trade winds for tomorrow look similar in strength, perhaps a touch lighter, and that should allow for sea breezes to develop on the leeward side of the islands.
For PMDY conditions look to remain dry, though we may get a few low to mid level clouds due to a low sitting north of the region. Opted to keep the forecast dry for the site on Monday, though the ECMWF model shows the potential for some passing showers Monday afternoon. Both the GFS and the ECMWF show showers late Monday into Tuesday, with winds shifting to the north or northwest.
For NSTU, models show passing showers through the TAF cycle, which may bring periods of MVFR cigs and vis.
Moderate to locally fresh trades will continue through Tuesday before strengthening through the latter half of the week. Moisture associated with a weak trough moving in on the trade wind flow may bring a slight uptick in shower activity today into Tuesday. Wednesday night, the remnants of Tropical Storm Norbert enter the offshore waters and are forecast to bring a more significant increase in moisture and stronger trade winds Thursday into the weekend.
Surf along south-facing shores will be slightly below seasonal average through Tuesday. A series of long-period swells are expected during the second half of the week. The first pulse will gradually fill in tonight into Wednesday out of the southwest, followed by larger south-southwest swells Friday into the weekend. Surf gradually trends upward through the week beginning Wednesday and will approach advisory thresholds by the weekend.
Surf along east-facing shores should see an increase during the second half of the week as the trades strengthen and the remnants of Tropical Storm Norbert move through the islands. Flat to tiny surf along north facing shores is expected through the forecast period.
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