textproduct: Honolulu

SYNOPSIS

Strong and gusty trade winds will prevail into Sunday as Hurricane Nolo moves toward the west well south of the islands. Deepening high pressure north of the state will produce drier and more stable conditions tonight and early Sunday, leading to continued strong wind gusts over and downwind of terrain, especially in west Maui and leeward Kohala on Big Island. The threat of flooding rainfall has diminished across Big Island and Maui County tonight, with drier conditions on Sunday leading to limited rainfall along windward slopes and dry conditions leeward. Trade winds will lower and shift out of the east-southeast Monday through Wednesday, and chances of rainfall will increase on Kauai and Oahu as moisture trailing Nolo moves over the western end of the island chain.

DISCUSSION

Strong and gusty trade winds are in place across most of the state as strengthening Hurricane Nolo is moving slowly westward less than 200 miles south-southwest of Big Island. A mid to upper level ridge building north of the state initiated the westward acceleration of Nolo and is creating some stability. A tight pressure gradient north of Nolo and the modest developing stability has produced conditions conducive for downsloping winds within the strong trade wind flow. As a result, Wind Advisory conditions prevail on Oahu and Kauai, and portions of Maui County downwind of terrain are experiencing gusts of around 70 mph or more, mainly in the area around Ukumehame, Olowalu, and Launiupoko. On Big Island, wind gusts nearing 60 mph are being observed in the Kohala Districts. Even though the Tropical Storm Warning for Big Island and Tropical Storm Watch for Maui County have been discontinued, the wind conditions necessitate that the Wind Advisory be expanded to all islands, while a High Wind Warning be posted for portions of Maui County and Big Island. The flood threat is diminishing, but ongoing rain on windward and southeast Big Island will require that the Flood Watch be extended through tonight for that island.

As Nolo moves westward tonight and Sunday, strong and gusty trade winds will persist due to the tight pressure gradient north of Nolo. The threat of heavy rainfall will diminish on Big Island overnight, with limited windward rainfall due across the rest of the state. Expect the Flood Watch to be down by morning.

Winds will ease Sunday afternoon or evening as the pressure gradient slowly relaxes in response to Nolo moving farther westward. Wind headlines may be dropped by Sunday evening or at least be scaled back to limited wind-exposed areas. Showers will be light and largely confined to windward slopes.

Winds will gradually decline and shift out of the east-southeast Monday through Wednesday. The latest National Hurricane Center forecast shows Nolo passing several hundred miles west of Kauai early next week, but it is worth monitoring the progress of the system for any changes to the forecast track. Model guidance shows a band of moisture trailing Nolo and possibly moving over the western end of the island chain Tuesday into Wednesday. If this occurs, Kauai and Oahu could experience an increase in rainfall.

In the long term, weaker trade winds and drier weather is favored by Thursday.

AVIATION

Gusty winds of 20 to 40 kt continue across most of the area with isolated higher gusts associated with Hurricane Nolo. Brief MVFR conditions are possible in any showers, mainly across windward and mountain areas especially in portions of Maui and Big Island (and Molokai and Lanai). Honolulu has and should continue to see more isolated passing showers.

AIRMET Sierra is in effect for mountain obscuration across entire area.

AIRMET Tango has been issued for moderate turbulence downwind of terrain due to the strong winds, with isolated severe turbulence also possible.

Tropical SIGMET Oscar covers Hurricane Nolo.

MARINE

As of 5 PM HST this evening, Hurricane Nolo was located near 16.7N 156.5W, approximately 165 miles south-southwest of South Point, and moving W at 7 knots.

The Tropical Storm Warning for the waters surrounding the Big Island and the Tropical Watch for the waters around Maui have been cancelled as Hurricane Nolo gradually accelerates westward south of the state. However, the pressure gradient between Nolo to the south and high pressure to the northeast will continue to drive strong to gale-force trade winds through Sunday and a Gale Warning has been issued for all of the Hawaiian coastal waters.

A combination of southeast swell originating from Hurricane Nolo and strengthening easterly trade winds is producing advisory level surf along east facing shores of the Big Island, Maui, Molokai, Oahu, and Kauai that will hold through tonight and then begin to diminish late Sunday into early next week as Nolo moves westward, then northwestward, and gains some distance from the islands. As it progresses on this track, the focus will shift to south facing shores as they receive at least a moderate bump to surf from Nolo on top of a moderate, long period south-southwest swell that began filling in earlier today and may approach advisory levels by Sunday afternoon.

A small, long period northwest swell began filling in earlier today and will continue to bring a small bump to north facing shores into early next week. A series of small, medium-period east swells are expected from Hurricanes Odalys and Polo in the East Pacific next week.

FIRE WEATHER

As Hurricane Nolo moves westward through Sunday, easterly winds will remain strong and gusty over and downwind of terrain, with very strong wind gusts in excess of 60 mph expected over portions of west Maui and leeward Kohala. Rainfall over the last month has led to some improvement in fuels, but the strong and gusty trade winds have been able to drive a wildfire in the Olowalu area of Maui, even with relative humidity remaining rather high at 60 to 70 percent. With drier and continued windy weather due on Sunday, wind and relative humidity will be at or near critical fire weather levels in many leeward locations, and the only factor against issuing a Red Flag Warning is the limited widespread readiness of fuels.

HFO WATCHES/WARNINGS/ADVISORIES

Wind Advisory until 6 PM HST Sunday for Niihau-Kauai Leeward- Kauai Mountains-Waianae Coast-Oahu North Shore-Olomana-Central Oahu-Waianae Mountains-Kahoolawe-Maui Windward West-Haleakala Summit-Big Island Interior-Kauai North-Kauai East-Kauai South- East Honolulu-Honolulu Metro-Ewa Plain-Koolau Windward-Koolau Leeward-Molokai North-Molokai West-Molokai Leeward South-Lanai South-Maui Central Valley North-Kipahulu-South Maui/Upcountry- Big Island Southeast.

High Surf Advisory until 6 PM HST Sunday for Olomana-Maui Windward West-Kauai East-Kauai South-Koolau Windward-Molokai Windward-Molokai Southeast-Windward Haleakala-Kipahulu-South Haleakala-Big Island East-Big Island North.

High Wind Warning until 6 PM HST Sunday for Lanai Mauka-Maui Leeward West-Kohala-Molokai Windward-Molokai Southeast-Lanai Windward-Lanai Leeward-Maui Central Valley South-Windward Haleakala-South Haleakala-Big Island South-Big Island North.

Flood Watch through late tonight for Big Island.

High Surf Warning until 6 AM HST Sunday for Big Island South-Big Island Southeast.

High Surf Advisory from 6 AM to 6 PM HST Sunday for Big Island Southeast.

Gale Warning until 6 PM HST Sunday for all Hawaiian waters.