textproduct: Honolulu

SYNOPSIS

Breezy to locally windy trades are expected through Friday, then moderate to breezy trades will persist through the weekend and deliver periodic showers to windward and mountain areas. Tropical Cyclone Fausto (or its remnants) may impact the state towards the middle of next week, but it's too early to determine potential impacts.

DISCUSSION

Radar and satellite imagery show drier air filtering across the state on the trade wind flow this afternoon, with isolated showers moving into windward and mauka areas. Robust high pressure to the far north will drive breezy to locally windy trades across the state through the end of the week. Trade wind speeds will then drop a notch to moderate to breezy levels this weekend as the high moves farther to the west. With deep ridging persisting over the region, a somewhat drier trade wind pattern is expected to persist through the weekend as shower activity is suppressed by subsidence. However, minor upticks can be expected during the overnight to early morning hours and when minor batches of moisture filter across the region.

Next week, weather across the state will depend on the eventual track and intensity of Tropical Cyclone Fausto. The National Hurricane Center is forecasting a gradual weakening of this system as it tracks westward and enters the Central Pacific this weekend, with further weakening expected early next week as it moves into a more hostile environment with cooler waters and increased shear. At this time, it remains too early to predict any direct impacts from wind or rainfall on Hawaii, though confidence is increasing in east-facing shores receiving a decent swell late this weekend into early next week. See the marine discussion below for more details.

AVIATION

High pressure north of the main Hawaiian islands will maintain moderate to strong trades into Friday. Winds are expected to weaken a bit Friday afternoon and evening. AIRMET Tango remains in place for mechanical turbulence to the lee of the mountains as a result. Anticipate this AIRMET to remain in place through Friday morning.

Some clouds and showers riding in on the trade wind flow will bring passing MVFR conditions mainly along windward mountain slopes. Otherwise, VFR conditions are expected to prevail.

MARINE

High pressure far north of the state will maintain fresh to locally strong trades through the weekend. A Small Craft Advisory (SCA) is in effect for all Hawaiian waters through Friday. Widespread fresh to strong winds are expected during this time with near gales possible for the windier waters around Maui County and the Big Island. The strong high to the north is expected to eventually shift westward and weaken some, which should allow the trade winds to weaken a notch this weekend and may lead to a reduction in area for the SCA beyond Friday. Trends in the strength and direction of winds early next week become less clear as a result of the uncertain track of a weakening Hurricane Fausto (forecast to become a tropical storm over the weekend) in the central Pacific.

The High Surf Advisory (HSA) has also been extended through Friday as a long-period south swell is forecast to peak tonight, with advisory level surf likely continuing into Friday as it begins to trend down. Friday night, it is possible that surf briefly falls below advisory criteria before another reinforcing long-period south swell arrives for Saturday and may push surf back up to advisory level. Regardless of whether there is a brief break or advisory level surf is maintained, there is potential for the HSA to be extended into the weekend. However, this next southerly pulse looks to be somewhat shorter period and lower energy than the last. The south swell will then slowly decline through the first half of next week.

Surf along east-facing shores will remain rough and choppy, supported by strong easterly trade winds combined with a small, medium-period east swell generated by former TC Elida. The latter swell fades through Friday while trade wind swell continues. This weekend, larger surf generated by Hurricane Fausto is possible and could bring advisory level surf along east facing shores by late Sunday into early next week.

Surf along north-facing shores will remain at flat to tiny levels through the weekend.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Advisory until 6 PM HST Friday for Big Island South- Big Island Southeast-East Honolulu-Ewa Plain-Honolulu Metro- Kahoolawe-Kauai South-Kauai Southwest-Kona-Lanai Leeward-Lanai South-Maui Central Valley South-Maui Leeward West-Molokai Leeward South-Niihau-South Haleakala-South Maui/Upcountry- Waianae Coast.

Small Craft Advisory until 6 PM HST Friday 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.