textproduct: Honolulu

SYNOPSIS

Several high pressure systems passing through the North Pacific basin will maintain a broad ridge north of the Hawaiian Islands for at least the next seven days. This ridge strength and position will maintain moderate to locally strong easterly trade winds across the region with only subtle day to day wind speed changes through next weekend. A narrow upper level trough with several embedded upper lows will remain anchored across the region keeping periods of trade wind showers in the forecast for the foreseeable future. These passing showers will favor windward and mountain areas in the overnight to early morning hours.

DISCUSSION

The infrared satellite picture this morning continues to show bands of unsettled cumulus clouds drifting into the islands on the easterly trade winds. Rainfall amounts will remain on the lighter side as each band of showers passes quickly through the island chain. Upper level troughing and lows embedded within this narrow upper trough will push back on the broad downward moving subsidence from the ridge north of the region, lifting temperature inversion heights into the 6,000 to 8,000 foot range over the next seven days. A wetter pattern than normal to start out our summer dry season.

Brief passing showers will develop over the islands into next weekend with day to day changes in easterly trade wind speeds. Overall expect moderate to locally strong trade winds to continue to blow across the Hawaii region into the foreseeable future.

Looking into the extended range model solutions there are some early hints at an unstable cloud band, the remnants of a dissipated East Pacific front, moving through the islands next Saturday. Additional lift for these unstable clouds along this band will be supported from a weak upper level low over the islands. The combination of low level instability and weak upper level forcing may increase cloud cover and shower activity statewide. Enhanced rainfall amounts in this pattern will remain on the lighter side as any shower bands will be moving through the islands fairly swiftly. The best chances for rain next weekend will fall between the Saturday evening to early Sunday morning time periods. Stay tuned as these wet weather impacts for next weekend will likely evolve as the forecast time period grows shorter.

AVIATION

Breezy to locally windy trades will continue for next few days. Low cigs and SHRA expected over windward and mauka locations. MVFR conds possible but VFR should prevail.

AIRMET Sierra is in effect for mtn obsc for windward locations of Oahu, Molokai and Maui.

AIRMET Tango is in effect for low-level turb over and downwind of terrain.

MARINE

Strong easterly trades will persist through tonight, then ease into the fresh to strong category through the first half of the week as the ridge weakens north of the state. This will allow the Small Craft Advisory to continue for all waters through tonight, then for the typically windier waters and channels from Monday through much of the week.

Surf along south facing shores will remain at similar levels today before gradually lowering Monday as a medium-period south swell lingers. This is supported by overnight observations at the NDBC 51002 buoy south of the islands, which depict a steady trend with peak energy centered around the 15-second band. A fresh long-period south swell will arrive Tuesday, then build to near seasonal average through midweek before slowly easing Thursday.

Looking ahead to later in the week, a more significant long- period south-southwest swell is expected due to a storm-force low currently located southeast of New Zealand. Satellite data shows a large fetch of 40 to 50 kt winds generating seas of 35 to just over 40 ft, focused toward Hawaii along the 190-degree directional band. Expect surf to begin building locally Friday with 20+ second forerunners, then peak above advisory levels next weekend.

Surf along exposed north and west facing shores will hold today before lowering Monday as a small north-northwest swell moves through. This is supported by overnight observations at the NDBC 51001 buoy northwest of the islands, which depict a steady trend with peak energy centered around the 13-second band. Late-season North Pacific activity will continue this week due to a storm- force low currently located around 2000 nautical miles northwest of the state and tracking northeastward toward the Aleutian Islands. Although the bulk of the energy will remain focused northeast of the islands, expect long-period forerunners to arrive Tuesday, with this source gradually building down the island chain thereafter. Above-average surf is likely by daybreak Wednesday near the peak before lowering Thursday.

Surf along east facing shores will remain rough through Tuesday, then gradually lower by midweek as the trades ease slightly.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters-Big Island Windward Waters.

Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.