West Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows around 75 near the shore to around 66 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Partly sunny. Breezy. Isolated showers late in the afternoon. Highs 86 to 91 near the shore to around 78 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Breezy. Mostly cloudy with isolated showers. Lows around 75 near the shore to around 66 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with isolated showers. Lows 71 to 78. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Friday: Mostly cloudy. Breezy. Isolated showers early in the morning. Scattered showers in the afternoon. Highs 80 to 89. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 72 to 78. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 70 in the valleys to around 62 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 74 to 82 in the valleys to around 68 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Friday Night: Windy. Mostly cloudy with scattered showers. Lows around 71 in the valleys to around 63 above 4000 feet. Northeast winds 10 to 25 mph with gusts to 45 mph increasing to 10 to 35 mph with gusts to 60 mph after midnight. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 66 to 76. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 40 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 71 to 88. East winds up to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 67 to 76. East winds up to 25 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 67 to 77. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Friday: Mostly cloudy. Breezy. Scattered showers early in the morning. Isolated showers in the late morning and early afternoon, then scattered showers late in the afternoon. Highs 78 to 86. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 68 to 77. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Hurricane Nolo will drift 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.

Discussion

Regional satellite imagery shows a typical trade wind pattern over the western half of the state this afternoon with somewhat limited showers focused windward and mauka. High clouds venting off of Hurricane Nolo have spread across the skies of Maui County and the Big Island. A weakly convergent west-east oriented band of showers extends from the Big Island and points well to the east. Convergence within this band is modeled to weaken with time, and radar imagery certainly supports that idea with very lackluster presentation on the South Point/PHWA radar this afternoon. Over Windward Big Island, showers are seen filling in from the NE on prevailing low-level trades. 12 hour rainfall totals generally about 1.5″ or less over windward portions of the Big Island with slightly lesser amounts for Windward Maui. Trades are currently gusting to around 15-25 mph in most locations with localized gusts approaching 40 mph in the typical windy zones of Maui County and the Big Island.
Deeper moisture is modeled to push onshore over the Big Island as the night progresses. Despite consensus on the position of Nolo and subsequent placement of deeper moisture, QPF is considerably different between the GFS and EC, particularly over the Ka'u District of the Big Island. At this stage, the aggressive EC presentation is difficult to believe given the lack of any organized activity upstream. Even the hi-res guidance is rather conservative in this area. Trended rainfall totals down accordingly. However, 90th percentile values remain quite high owing to those ensemble members that still draw Nolo further north and engulf that area in the deep tropical moisture around the core of the system itself. Though increasingly unlikely, this possibility precludes lowering forecast rainfall for Ka'u much more than already done. Should be a fairly straight forward forecast otherwise with strengthening NE winds driving moderate to heavy showers over windward portions of the Big Island and Maui as moisture deepens and spreads northward.
Primary decision point in the forecast going forward is handling of wind headlines for those islands outside the existing tropical watches and warnings. A High Wind Watch for very strong trades may be warranted for Oahu for Saturday and Saturday night if the forecast track holds. A Wind Advisory is more likely for Kauai during this same time. With plenty of lead time yet to work with, will hold off on issuing any wind headlines at this time. The Hurricane Watch and Tropical Storm Warning remain in effect for the Big Island and the Tropical Storm Watch continues for Maui County.
By the middle of next week, troughing will draw Nolo sharply north or northeastward west of Kauai. The end of next week will then feature light S/SE flow as Nolo lifts north of the area and gradient over the state weakens substantially.

Aviation

Breezy and gusty trade winds are expected to continue as Hurricane Nolo continues its slow approach towards the Big Island. Winds will strengthen tomorrow especially over the eastern half of the state. MVFR to IFR conditions are expected tonight through tomorrow for windward Big Island due to increasing showers. LIFR is possible within the heaviest showers. Thunderstorms cannot be ruled out for the Big Island as well, but probabilities remain low. Elsewhere, showers and associated MVFR conditions are expected to remain focused over windward and mountain areas through tomorrow.
AIRMET Sierra is in effect for mountain obscuration for windward areas of Kauai, Maui, and the entire Big Island. This AIRMET will likely be expanded to include other areas as Hurricane Nolo continues its approach.
AIRMET Tango remains in effect for moderate turbulence downwind of island terrain due to breezy trade winds. Expect this to continue through the forecast period.
TC SIGMET series Oscar covers Hurricane Nolo.

Marine

Hurricane Nolo is located about 270 miles south of the Big Island this afternoon. It is expected to continue strengthening over the next few days as it tracks slowly northward through Friday, then turns west passing south of the Hawaiian Islands this weekend. Marine impacts will include increasing winds, waves, and rainfall chances across the coastal waters through the weekend. As of this afternoon, a Tropical Storm Warning and Hurricane Watch continues for waters surrounding the Big Island, including the Alenuihaha Channel, a Tropical Storm Watch remains in effect for the waters of Maui County, and a Small Craft Advisory remains in effect for the rest of the coastal waters and channels near Kauai and Oahu.
For the western islands, the current small south swell will continue to fade as another small overlapping southwest swell builds in from Friday into the weekend. Meanwhile, Hurricane Nolo will likely produce a southerly swell reaching advisory thresholds for exposed south facing shorelines, initially for the Big Island, then potentially expanding westward across the state later this weekend. Additionally, strong trades will likely result in advisory level surf for east-facing shores for the eastern islands tonight into Friday, potentially expanding to remaining islands later Friday into the weekend as winds continue to expand westward. Based on buoy and surf observations this afternoon, a High Surf Advisory has been issued for east facing shores of Molokai and Maui and for east and southeast shores of the Big Island.
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. Finally, dangerously large wind waves will produce a rough and choppy sea state for much of the area over the next few days, with the largest waves (which could exceed 20 feet in some locations) expected around Maui County and the Big Island.

Fire weather

Winds will steadily as Hurricane Nolo moves closer. By Friday, very strong winds are possible on Big Island 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.
Tropical Storm Watch for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala.
High Surf Advisory until 6 PM HST Saturday for Maui Windward West, Molokai Windward, Molokai Southeast, Windward Haleakala, Kipahulu, South Haleakala, Big Island Southeast, Big Island East, Big Island North.
Hurricane Watch for Big Island,
Tropical Storm Warning for Big Island,
Tropical Storm Watch for Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel.
Hurricane Watch for Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Tropical Storm Warning for Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters.

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Data Courtesy of NOAA.gov