Lighter background winds will support daytime sea breezes and nighttime land breezes from Wednesday through Friday. Thus, most cloud cover and shower activity will favor interior and mountain areas during the afternoons. In addition, deeper moisture associated with a weak trough will move northward from the southeast Wednesday through Friday, and will briefly increase shower chances island-by-island as it weakens. A more typical trade wind pattern will return late this weekend.
This afternoon, mostly dry and stable conditions are prevailing across the main Hawaiian Islands. Latest satellite and radar imagery shows isolated light showers across the region, and statewide rain gauge networks have largely reported little to no rain today. The exception is over Kauai and Niihau, where showers have been slightly more persistent than elsewhere in the state. A late morning advanced scatterometer pass, as well as surface observations, show that moderate trade winds are prevailing.
As a series of fronts move across the North Pacific well north of the island chain, moderate trade wind flow will become disrupted, further weakening winds across the region. Daytime heating, combined with weak background surface flow, will lead to daytime sea breezes and nighttime land breezes for the next few days. Clouds and showers should mainly be limited to over the island interiors and mountainous terrain, particularly during the day. The one caveat in the forecast, however, is that a weak surface trough is currently located southeast of the Big Island. Latest hi-res guidance and global models depict this weakening feature to move northward in the vicinity of the eastern end of the state on Wednesday. As a result, shower activity will likely increase over the Big Island tomorrow, especially compared to what was experienced today. This trough will continue lifting north, and is progged to be located just east of Maui by Wednesday evening. As the trough moves northward, expect increased showers for portions of Maui County late Wednesday into Thursday, and possibly for Oahu as well by Thursday afternoon. The weakened feature will then continue to dissipate as it moves away from the state.
After a brief period of east-southeasterly flow Saturday, moderate easterly trades will return during the second half of the weekend. Fairly dry conditions will limit windward shower coverage into early next week.
Moderate trade winds continue through the evening before weakening tomorrow. A surface trough SE of the Big Island will progress northward, bringing enhanced shower activity to windward sections of the Big Island and possibly Maui tomorrow morning. Afternoon cloud and shower development is possible across leeward areas of the state as well. Expect MVFR conditions within showers, and brief IFR conditions within heavier showers.
AIRMET Sierra is in effect for mountain obscuration for NW - E sections of Kauai. Expect these conditions to diminish overnight. AIRMET Sierra may be expanded to cover at least windward Big Island when the showers associated with the trough arrive.
No other AIRMET's are in effect nor anticipated.
A ridge of high pressure north of the state is driving moderate to locally fresh trades. Trades will ease to light to moderate speeds Wednesday as the trough pushes the ridge east of the state. The ridge will strengthen north of the area over weekend as the trough weakens and lifts far north, allowing moderate to fresh trades to return.
The large, long period south southwest swell that brought warning level surf to the state earlier this week will continue to slowly decline. A High Surf Advisory (HSA) remains in effect through tonight for all south facing shores. Surf heights are expected to drop below advisory levels by Wednesday. Another moderate, long period, south southwest swell is expected to fill in Wednesday night into Thursday that could push surf back up to HSA levels along south facing shores. This swell will slowly fade Friday through the weekend.
Surf along north facing shores will remain flat to tiny through the forecast period. Surf along east facing shores will remain below average as easterly trade winds ease through the end of the week.
The Coastal Flood Statement has been extended through tonight for minor coastal flooding of vulnerable low-lying coastal roadways, docks, boat ramps and other coastal infrastructure due to King Tides. King Tides combined with water levels that are running higher than predicted will lead to minor flooding potential around the daily peak tide, which will be during the late afternoon and early evening hours. While minor coastal flooding is expected along all shorelines, the combination of the large south southwest swell and peak daily high tides will make low- lying coastal areas along south and west shores susceptible to more widespread coastal flooding through this evening.
A Marine Weather Statement has also been extended through tonight due to the moderate-to-long, long-period south southwest swell producing harbor surges and breaking waves near harbor entrances along south and west- facing harbors.
High Surf Advisory until 6 AM HST Wednesday for Niihau-Kauai Leeward-Waianae Coast-Kahoolawe-Maui Leeward West-Kona-Kohala- Kauai South-East Honolulu-Honolulu Metro-Ewa Plain-Molokai Southeast-Molokai Leeward South-Lanai Leeward-Lanai South-Maui Central Valley South-Kipahulu-South Maui/Upcountry-South Haleakala-Big Island South-Big Island Southeast.
