textproduct: Honolulu

SYNOPSIS

A high pressure ridge north of the state will maintain trade winds over the region through much of the week. Some weakening in the trades is expected by the weekend. An upper level low approaching from the west could enhance shower activity this weekend.

DISCUSSION

No changes to the forecast with the afternoon package, and the forecast philosophy remains the same. A high pressure ridge north of the area will maintain a trade wind pattern through the week. Moderate to locally breezy trades are expected to continue for another couple of days, with subtle changes in the winds speeds.

An upper level low about 700 miles northwest of Kauai will continue move towards the islands this week. As it approaches the islands Friday, a surface trough forming near the islands will help to disrupt the trade wind flow a bit, weakening winds to more moderate levels, and with some areas possibly seeing winds turn a little to the southeast. Global models continue to be in good agreement with moisture bands continuing to ride in on the trade winds through the week, so expect typical trade winds showers to mainly impact windward and mauka locations. In this pattern, afternoon showers of the Kona slopes are also likely.

Heading into the weekend when the upper low is moving over the northern islands, there could be some enhancement to the trade wind showers. The model thunderstorm probabilities remain near zero, so not expecting any thunderstorm activity.

During the start of the new week, as the upper low moves north of the Big Island, upper level winds near the summits could increase, but at this time are expected to remain below advisory levels.

AVIATION

Breezy trades continue through the period delivering periods of low clouds and showers windward and mauka. A band of showers advancing over Oahu this afternoon is beginning to clear the island and the attendant AIRMET has therefore been expired. Otherwise, expect the typical nocturnal maximum in shower coverage and prevailing VFR leeward.

AIRMET Tango for low-level lee turb remains in effect.

MARINE

A surface ridge north of the state will maintain breezy to strong trade winds across the Hawaiian coastal waters through at least Wednesday 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, has been extended through Wednesday night, then will likely be scaled back later in the week to the typically windier waters around the Big Island and Maui County.

The current south swell will continue to fade while the next pulse of south swell energy arrives tonight, providing a slight boost to south shore surf through midweek. However, a more significant 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 Hawaiis 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.

Forerunners from a small, long-period northwest swell began filling in along north-facing shores this morning. Although the bulk of the energy from this swell will remain focused northeast of the islands, it is expected to peak locally late tonight into Wednesday, raising surf to above-seasonal-average heights before gradually subsiding into the weekend.

Surf along east-facing shores will remain rough through midweek, then gradually lower later in the week as the trades ease.

HFO WATCHES/WARNINGS/ADVISORIES

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.