High pressure ridging will generally influence island weather behavior the next several days. A weak low will approach Hawaii from the west today and pass over the state Friday. Troughing leading this weak feature will weaken recently breezy trades and initiate more widespread showers Thursday and Friday. Any measurable rain will have low accumulation over the majority of the state. Weak troughing within a fairly dry air mass indicates stable enough conditions to support little to no precipitation through early June.
Not much fanfare weatherwise for us here in paradise the next several days. Troughing ahead of a weak low in the vicinity of the western half of the Hawaiian archipelago will move over us Friday and transform into a open wave this weekend on its northeastern trek. The mid to upper level low in itself will hardly leave a mark upon its passage over the state Friday. The leading trough ahead of it will be what will increase moisture from current below normal values to near normal levels tomorrow (Thursday). This will moisten a slightly deeper boundary layer over the next few days; from near 8k ft inversion bases today to around 9k ft in depth tomorrow. This subtle uptick in moisture may be enough to thicken up clouds and increase areal shower coverage from early tomorrow morning through Friday morning. This leading trough will disrupt the strong pressure gradient back from the large broad 1038 mb surface high paralleling 40N across the eastern two thirds of the central Pacific. The result will be weakening trades beginning today with this downward trend occurring through the remainder of the week. The highest Thursday and Friday (24 to 36 hour) QPF will likely be between a half an inch to an inch along better windward exposures and within higher terrain.
Less cloudy and even drier weather will prevail this weekend as the weak trough exits stage right. General troughiness over the North Pacific will dominant island weather going into the month of June. Typical wet windward exposures and slopes will still pick up their seasonal daily rainfall with higher amounts occurring overnight. Drier air by early June standards will filter in from the north. Trades will be lighter due to a weaker pressure gradient as northern surface troughing splits the high cells well north of the area. While winds will be lighter, they should still stay up enough to help mix out lower level afternoon humidity. Other than the diurnal trend of overnight windward-focused trade showers, the last couple of days of May and the first week of June will fall in line with dry season climatology.
Breezy trade winds will continue today, with periods of low clouds and showers favoring windward and mountain locations. Although MVFR ceilings and visibilities may be possible within passing showers at times, VFR flight conditions will prevail for most locations. Showers will be most prevalent during the overnight through morning hours.
AIRMET Sierra is in effect for mountain obscuration along N through SE sections of Kauai, Oahu, and Molokai this morning due to low clouds and passing showers.
AIRMET Tango remains in effect for mod low-level turbulence over and downwind of terrain across all islands. This AIRMET will likely be needed through tonight.
A surface ridge north of the state will maintain breezy to strong trade winds across the Hawaiian coastal waters through at least tonight before a weakness develops in the ridge, allowing trade wind speeds to ease slightly during the latter part of the week into the weekend. The Small Craft Advisory (SCA), which currently encompasses all Hawaiian coastal waters remains in effect through tonight, then will likely be scaled back in area later in the week to the typically windier waters around the Big Island and Maui County. A more significant weakening of the trade winds is likely this weekend into early next week as a large North Pacific low pressure system far north of the islands breaks the ridge down even further.
Offshore buoy observations suggest that a small, long-period northwest swell will peak this morning for Kauai and Oahu, and later this afternoon/tonight for Maui and the Big Island as it moves down the island chain. North and west facing shores will see moderate surf at the peak before gradually subsiding into the weekend.
A medium-period south swell will continue to bring small surf to south facing shores through Thursday. A more significant long-period south swell is expected to begin filling in Thursday night and will likely bring above-advisory-level surf to south-facing shores through the weekend. This swell originated from a storm-force low that passed south and east of New Zealand over the weekend, generating seas of 35 to 40 feet or greater within Hawaii’s swell window, though the peak of the energy may pass just east of the state. Elevated surf will likely continue into the first week of June due to a continued active weather pattern near New Zealand sending swells toward Hawaii.
Surf along east-facing shores will remain rough through Thursday, then gradually lower Friday into the weekend as trade winds ease.
Small Craft Advisory until 6 AM HST Thursday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Big Island Windward Waters-Kaiwi Channel-Kauai Channel-Kauai Leeward Waters-Kauai Northwest Waters-Kauai Windward Waters- Maalaea Bay-Maui County Leeward Waters-Maui County Windward Waters-Oahu Leeward Waters-Oahu Windward Waters-Pailolo Channel.
