A cold front will move across Kauai and Oahu tonight into early Wednesday, then stall across the central islands late Wednesday through Thursday. This will bring periods to showery weather to most islands this week. More unsettled weather is possible Friday through the weekend as a plume of deep moisture develops along another front as an upper-level disturbance moves across the state. Drier weather and improving conditions are then expected early next week as ridging builds across the region.
Satellite imagery shows a cold front approximately 100 miles west- northwest of Kauai this afternoon. Moisture ahead of the front is resulting in pockets of clouds and showers across the western islands. Elsewhere, localized sea breezes due to light to moderate east-southeasterly flow is producing some clouds over island interiors. Expect little change through this evening.
Guidance continues to show the front moving towards the state this afternoon, then across Kauai late this evening and Oahu by early Wednesday morning. The progressiveness of the front should slow considerably later tonight as the mid-level flow becomes parallel to the front. Nonetheless, expect an uptick in clouds and showers across the western islands tonight into early Wednesday, with breezy northerly winds developing in the wake of the front.
Guidance then shows the front stalling over the central islands late Wednesday through Thursday as a shortwave trough moves overhead. The will help to maintain clouds and showers across most islands, with some enhanced showers possible over windward and mauka areas of Oahu and Maui County.
Late in the week and over the weekend, the model solutions, their ensembles, as well as the AI versions of both the GFS and ECMWF suggest some more uncertainty in the forecast. Overall, the pattern appears to favor a somewhat unsettled period as moisture pulls along the stalled out frontal boundary and upper level troughing moves overhead. Improving conditions are then forecast for early next week as deep layer ridging builds over the island chain.
Light to moderate east-southeasterly winds will keep a land and sea breeze pattern in place in advance of a cold front that is expected to reach Kauai late this evening, Oahu early Wednesday morning, and then stall out somewhere over the central part of the state. Showers are expected to increase near the frontal boundary, with breezy northerly winds in its wake. Mainly VFR conditions will prevail in advance of the front, then some brief MVFR cigs/vsbys could develop near the frontal boundary in showers.
AIRMET Tango is in effect for moderate upper level turbulence between FL310 and FL370 due to jet stream winds. AIRMET Sierra may be needed for mountain obscuration for Kauai and Oahu overnight.
Gentle southerly winds will give way to a front that will produce a brief period of fresh to strong northerly winds and elevated rough seas around Kauai tonight. North to northeast winds associated with the front will weaken as the feature passes over Oahu on Wednesday then stalls across Maui County waters Wednesday night. Around the Big Island, expect continued gentle east to southeast winds. A Small Craft Advisory (SCA) has been issued for waters around Kauai for tonight, and although we do not anticipate expanding the SCA, there is some chance it could be issued for Oahu waters on Wednesday morning. A surface ridge will develop about 100 nm north of Kauai on Thursday, leading to gentle to moderate easterly trade winds through at least Friday. Winds will turn out of the southeast and south during the weekend as another front approaches. A disturbance aloft could trigger heavier showers and possibly thunderstorms during this time.
Overlapping west-northwest to north-northwest swells will produce surf around High Surf Advisory (HSA) levels for exposed north and west facing through Friday. The latest west-northwest swell is filling in around Kauai and Oahu this afternoon after building to around 6 to 7 feet at 14 to 15 seconds at the NOAA buoys northwest of Kauai today. Expect this swell to generate surf just below HSA levels along north and west shores of Kauai and Oahu during its peak tonight, with gusty winds along the front producing rough conditions on Kauai and possibly on Oahu closer to daybreak. Overlapping pulses of west-northwest swell, similar in size, will arrive later Wednesday and keep surf near advisory levels, mainly on Kauai and Oahu, through Friday. A sharp downward trend and shift out of the north-northwest is expected during the weekend, followed by a potentially large northwest swell next Tuesday.
East shore surf will remain below seasonal average through the week, though a brief increase is possible on Kauai tonight due to strong northerly winds behind the front. Surf along south facing shores will remain very small through the week.
Small Craft Advisory until 6 AM HST Wednesday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters- Kauai Channel.
