textproduct: Honolulu

SYNOPSIS

Tropical Storm Nolo will intensity to a hurricane as it drifts northward toward Big Island through Friday night. Deepening moisture along the northern edge of the system will gradually increase rainfall across the Big Island and Maui, leading to the potential for significant flash flooding on windward and southeast Big Island. Big Island remains under a Hurricane Watch with the potential for damaging winds Friday and Saturday, and locally windy trade winds will develop across the rest of the island chain Friday. Nolo is expected to move westward on Sunday, but all interests in Hawaii should monitor the progress of the system as impacts could persist through the weekend.

DISCUSSION

Tropical Storm Nolo continues to slowly intensify less than 300 miles south of Big Island and is poised to begin a slow turn northward today. Locally breezy and gusty trade winds remain in place early this morning, with a few typically windy leeward sites measuring gusts in excess of 30 mph. Expect a slight upward trend in winds today as an intensifying Nolo gradually tightens the local pressure gradient. The bulk of the deeper moisture along the northern periphery of Nolo has remained just south of the Big Island coastal waters overnight, which has resulted in mainly light to moderate rain rates on windward Big Island. Most sites in this area have measured less than 1 inch of rainfall during the past 12 hours, though a few gages upslope of Hilo picked up 1.5 to 2 inches. The bulk of model guidance shows little change in rainfall through morning followed by increased chances of heavy showers this afternoon or evening.

Significant impacts could develop as early as Friday, mainly across the eastern end of the island chain, and will likely continue into the weekend. The National Hurricane Center track contains more uncertainty than normal, but confidence is high that Nolo will be at hurricane strength as it nears Big Island late Friday and eventually turns toward the west Saturday. A Hurricane Watch remains posted for Big Island, where damaging winds are a threat. Elsewhere, a Tropical Storm Watch may eventually be needed for some areas, namely Maui County, but at minimum, increasing trade winds will require a Wind Advisory. A Flood Watch remains posted for Big Island and Maui County. As slow-moving Nolo edges closer, deep moisture will increase rain rates over these islands, and the greatest concern is focused on windward and southeast Big Island, where a prolonged period of heavy showers and thunderstorms could produce widespread rainfall totals in excess of 20 inches.

The hurricane is expected to move westward Sunday, but given the high uncertainty in the official forecast track, impacts may persist through the weekend for some areas. More typical trade wind weather is expected early next week.

AVIATION

Breezy and gusty trades through the next 24 hours. Tropical Storm Nolo is about 290 miles south of the Big Island moving N at 2 kts. As this gets closer expect winds to increase especially across the eastern end of the state. Showers will increase and be heavy at times. TSTMs are possible but confidence is low on exactly where as such elected not to include those in the TAFs at this time. While conds are MVFR/VFR now, conds will deteriorate as Nolo nears. LIFR to MVFR possible across the Big Island and Maui with areas on the western end of the state being MVFR/VFR.

TC SIGMET Series Oscar covers Tropical Storm Nolo.

AIRMET Sierra is in effect for mtn obsc for Oahu, Molokai, Maui, and the Big Island. Expect this to expand as Tropical Storm Nolo gets closer.

AIRMET Tango is in effect for low level turb lee of terrain.

MARINE

Tropical Storm Nolo continues to strengthen this morning as the storm system is forecast to slowly drift northward towards the Big Island. Impacts with Nolo include increasing south and east swell, winds and rainfall lasting through the weekend. Marine impacts will highly depend upon the final track and intensity as Nolo continues to approach the Big Island from the south. Nolo is currently expected to continue on a slow northward trend through Friday with increasing waves along exposed south facing shores of the Big Island, before a forecast turn to the west this weekend with potential wind, weather and wave impacts to all coastal waters through the weekend.

The Hurricane Watch continues for waters surrounding the Big Island this morning, including the Alenuihaha Channel. A Small Craft Advisory remains in effect for the rest of the coastal waters and channels. A Gale Watch was added starting on Friday for the Pailolo Channel and Maalaea Bay due to strengthening trade winds.

The current small south swell continue to fade, as another small overlapping southwest swell builds in from Friday into the weekend. Tropical Storm Nolo is expected to strengthen into a hurricane later today, and will likely produce a southerly swell into at least High Surf Advisory thresholds for exposed south facing shorelines, initially for the Big Island and then a brief period of higher surf expanding westward across the state later this weekend as the center of Nolo drifts westward and passes just south of the Hawaiian Islands.

A new small, long period, northwest swell will fill in this weekend keeping surf slightly elevated along north and west facing shores into early next week. East facing shores will maintain rough, short period wind waves generated from the strengthening trade winds.

FIRE WEATHER

Winds will steadily strengthen as intensifying Nolo moves closer. By Friday, very strong winds are possible on Big Island, which remains under a Hurricane Watch, though heavy rainfall will likely mitigate fire danger over most areas. From Kauai to Maui County, rainfall over the last month has led to some improvement in fuels, but the gusty trade winds will produce moderate fire weather conditions over drier leeward areas through the weekend.

HFO WATCHES/WARNINGS/ADVISORIES

Flood Watch through Saturday afternoon for Lanai Mauka-Kahoolawe- Maui Windward West-Maui Leeward West-Haleakala Summit-Kona- Kohala-Big Island Interior-Big Island Summits-Molokai-Lanai Windward-Lanai Leeward-Lanai South-Maui Central Valley North- Maui Central Valley South-Windward Haleakala-Kipahulu-South Maui/Upcountry-South Haleakala-Big Island South-Big Island Southeast-Big Island East-Big Island North.

Hurricane Watch for Big Island-

Hurricane Watch for Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters.

Small Craft Advisory from 6 AM Friday to 6 PM HST Saturday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters.

Small Craft Advisory until 6 PM HST Saturday for Kauai Channel- Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters.

Small Craft Advisory until 6 AM HST Friday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters- Big Island Leeward Waters-Big Island Southeast Waters.

Gale Watch from Friday morning through Saturday afternoon for Maalaea Bay-Pailolo Channel.