A weakening cold front will bring moderate trade winds and a brief increase in clouds and showers, mainly over windward and mauka zones, on Wednesday. Otherwise, stable conditions and light winds, will limit rainfall.
Discussion
A surface ridge north of the islands, and mid level ridging over the islands, maintains the light wind, dry and stable airmass over the region. Expect limited shower through Tuesday with an inversion remaining around 3500 feet. Light winds will lead to land and sea breezes. Despite the dry conditions, some afternoon clouds are likely to develop, but very few showers are expected.
A cold front to the northwest of islands will push to the east, pushing the surface ridge over the islands further weakening our winds. This front is associated with a strong low far north of the islands. The southern end of the front is expected to weaken as it approaches the islands Tuesday night. What remains of the front will reach Kauai and Oahu very early Wednesday morning, and the remaining islands that afternoon into the Wednesday night. The front will bring moderate northerly winds and a brief uptick in windward showers. While the ridging aloft will weaken some during this time, it will still be in place, limiting shower development. Expect winds to veer to the northeast and increase a touch behind the front, before turning more to the east and weakening Wednesday night through Thursday.
There is good model agreement between the ECWMF and GFS that the zonal pattern aloft will break down during the second half of the week. That being said, at least through the weekend high pressure aloft remains over the islands, so we won't likely see any significant changes to our weather. Expect the second half of the week to be a return to lighter winds and relatively dry conditions.
Aviation
ARTICLE CONTINUES BELOW AD
The air mass over the state is expected to remain unusually stable. A strong inversion around 03 kft above the surface is inhibiting most precipitation. Late night satellite imagery reveals broad areas of thick stratocumulus across all the smaller islands and coastal Big Island as well. Mountain obscuration could become an issue for portions of Maui, Molokai, or Oahu later this morning. Good VFR is expected statewide in the afternoon.
A dying weather front will move in from the northwest early Wednesday. Layered clouds and light precipitation are expected to develop Kauai towards midnight tonight and across Oahu by Wednesday morning. Elsewhere, light and variable winds, patchy low clouds, and little or no precipitation will prevail.
Marine
The active pattern across the northern Pacific will continue to impact the Hawaiian waters through the upcoming weekend. The latest surface analysis reflects this and shows a hurricane- force low centered around 1300 nautical miles to the north, with its attendant cold front extending southwestward to around 400 nautical miles northwest of Kauai. Satellite-derived winds and seas on the backside of this system showed a decent sized area of strong gales to hurricane-force winds with seas above 40 ft focused at the local waters. A SOFAR drifter buoy near the head of the fetch (around 900 nautical miles north-northwest of Kauai) is peaking this morning well above predicted, but appeared to be on track with regard to the arrival time. As a result, seas will quickly ramp up over the local waters and exceed the Small Craft Advisory level of 10 ft beginning tonight as a significant northwest swell associated with this system arrives and moves through.
Surf along exposed north and west facing shores will hold steady below the advisory level today, then rapidly build and exceed warning levels late tonight through early Wednesday as the aforementioned northwest swell arrives. This source will peak well above warning levels through the day Wednesday, then begin to ease as the swell shifts out of the north late Thursday through Friday. As this source continues to ease, a new long-period northwest swell associated with the system currently developing east of Japan arriving Friday night into Saturday will steadily build and peak by the end of the weekend. Impacts associated with this type of event with back to back swells continuing for several days will only exacerbate ongoing erosion issues. In addition to the erosion issues, water sweeping over beaches may periodically reach roadways on Wednesday as the swell peaks.
Surf along south facing shores will remain at background levels throughout the week. Surf along east facing shores will generally remain small with exception for areas exposed to northerly swells. These areas will see significant increase with the extra- large north-northwest swell aforementioned above.
Winds will remain light and variable with land and sea breeze conditions prevailing this morning. Winds will shift out of the northwest this afternoon, then out of the north tonight into Wednesday and increase into the moderate to fresh category as high pressure builds north of the area in the wake of a passing cold front. By Thursday, the winds will shift out of a more typical easterly direction and hold in the moderate to fresh range. A downward trend with a shift out of the southeast is possible Friday into the weekend as the progressive pattern continues.
HFO Watches/Warnings/Advisories
High Surf Warning from midnight tonight to 6 PM HST Thursday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory from midnight tonight to 6 PM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters.
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