West Side

Today: Breezy. Partly sunny with isolated showers in the morning, then cloudy with frequent showers in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 79 to 87. East winds up to 20 mph. Chance of rain 80 percent.

Tonight: Breezy. Cloudy with occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 72 to 79. Northeast winds up to 20 mph becoming 10 to 15 mph after midnight. Chance of rain 90 percent.

Labor Day: Cloudy with frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 81 to 88. East winds up to 15 mph. Chance of rain 90 percent.

South Side

Today: Partly sunny in the morning, then cloudy with frequent showers in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 88. North winds up to 15 mph. Chance of rain 80 percent.

Tonight: Cloudy with occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 73 to 81. North winds up to 15 mph. Chance of rain 80 percent.

Labor Day: Cloudy with frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 90. North winds up to 15 mph. Chance of rain 90 percent.

North Shore

Today: Breezy. Frequent showers. Locally heavy rainfall possible in the afternoon. Highs around 82 near the shore to 68 to 73 near 5000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 74 near the shore to around 60 near 5000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Labor Day: Breezy. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 83 near the shore to 69 to 74 near 5000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Central Maui

Today: Breezy. Partly sunny with isolated showers in the morning, then cloudy with frequent showers in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 81 to 88. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 80 percent.

Tonight: Breezy. Cloudy with occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 75. East winds up to 20 mph. Chance of rain 90 percent.

Labor Day: Breezy. Cloudy with frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 83 to 90. Northeast winds up to 20 mph. Chance of rain 90 percent.

Upcountry

Today: Scattered showers in the morning, then frequent showers in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 71 at the visitor center to around 68 at the summit. Southeast winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 58 at the visitor center to around 48 at the summit. East winds up to 15 mph increasing to 10 to 20 mph after midnight. Chance of rain near 100 percent.

Labor Day: Cloudy with frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 73 at the visitor center to around 70 at the summit. Southeast winds up to 15 mph. Chance of rain 90 percent.

East Maui

Today: Breezy. Frequent showers. Locally heavy rainfall possible in the afternoon. Highs around 82 near the shore to 68 to 73 near 5000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 74 near the shore to around 60 near 5000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Labor Day: Breezy. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 83 near the shore to 69 to 74 near 5000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Lanai City

Today: Partly sunny in the morning, then cloudy with frequent showers in the afternoon. Highs 78 to 85. Northeast winds up to 15 mph. Chance of rain 80 percent.

Tonight: Cloudy with occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 69 to 74. Northeast winds up to 15 mph. Chance of rain 90 percent.

Labor Day: Cloudy with frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 79 to 86. East winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 90 percent.

Kaunakakai

Today: Partly sunny with isolated showers in the morning, then cloudy with frequent showers in the afternoon. Highs 77 to 90. East winds 10 to 15 mph. Chance of rain 80 percent.

Tonight: Cloudy with occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 64 to 78. East winds 10 to 15 mph. Chance of rain 90 percent.

Labor Day: Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 78 to 91. East winds 10 to 15 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

Breezy east-northeast trade winds will gradually veer to the east and then east-southeast this weekend into the upcoming week as Hurricane Lowell approaches from the southwest. Lowell is forecast to pass west of Kauai's coastal waters as a category 2 hurricane, and a Tropical Storm watch is in effect for Kauai and Niihau. Impacts such as high surf and heavy rain are forecast to extend hundreds of miles from the center, potentially impacting any of the islands.

Discussion

Radar and satellite imagery this morning show a wetter than normal trade wind pattern with numerous showers over windward and mountain areas. Moisture has already increased across the area more than forecast, and this is contributing to the increase in showers. Several windward areas have already picked up over 1.5 inches of rainfall in the past 6 hours. Although there may be a diurnal decrease in showers this afternoon, there is also a chance for thunderstorms on Big Island, which would of course come with high rain rates. The start time of the Flood Watch has been moved to noon from 6 PM HST today (beginning 6 hours earlier) to account for the early arrival of the better moisture.
Hurricane Lowell is currently sitting about XXX statute miles south-southwest of Kauai moving northwest at X mph as a category 4 (XXX mph maximum sustained winds). Lowell is forecast to continue a generally northerly track today, and then move north-northeast tonight through Monday. Its forward speed will increase today and tomorrow, and it is forecast to make its closest approach to Kauai County Monday night as a category 2 hurricane. Lowell is forecast to pass 100 to 200 miles west of Kauai, and will bring several hazards to the state. The main hazards are expected to be flash flooding, strong winds, and high surf. A Tropical Storm watch is in effect for Kauai and Niihau and its associated waters. A Flood Watch is now in effect from noon today through the end of Tuesday for all islands.
The greatest risk for flooding is from this afternoon through Tuesday morning, and could potentially linger into Wednesday. Deep tropical moisture has been brought north by the circulation around Lowell. The environment will begin destabilizing Sunday afternoon as CAPE values and moisture depth increase. Thunderstorms were already in the forecast starting tonight, but have been moved up to this afternoon over the Big Island. Kauai and Niihau are expected to receive the highest rain totals. However, the threat of heavy rainfall and thunderstorms will be present across the entire state starting this evening. Therefore everyone in the state should be prepared for potential flash flooding. A flood watch is in effect statewide from this afternoon through Tuesday.
Winds will increase and veer from east to southeast tonight through Monday. Kauai County will of course have the strongest winds because it is closest to Lowell. Winds will increase for the rest of the islands to a lesser extent, but will see local amplification by terrain.
The threat of short-lived, fast-moving tornados/waterspouts will be present mainly near Kauai and Niihau as Lowell makes its closest approach to the islands. These would likely be embedded in rainbands. This is due to the islands proximity to Lowell's east side, where low level shear and instability will increase as the center of circulation passes west of Kauai. On Monday, 0-1 km shear increases to 20-25 kt or more on Kauai and Niihau, and 0-1 km SRH increases for a time to 200-300 m2/s2 in the RRFS. The threat appears lower on other islands, though local maxima may occur in downwind convergence zones extending off the islands. This threat should decrease quickly early Tuesday morning.
For surf and other marine impacts, please see the marine section of the discussion below.
Any deviation in track or intensity could also change how these hazards effect the islands.
High pressure is forecast to build back in Thursday through Saturday, bringing in drier and more stable conditions. Long range models then indicate a tropical wave potentially moving over the islands next Sunday into Monday, although confidence is low this far out.

Aviation

Tropical moisture will deepen over the next 24 hours as wind directions aloft shift from a more southerly direction in response to Hurricane Lowell's northward track passing just west of Kauai. This unstable tropical air mass will produce increasing clouds and showers across the state with the highest chances for MVFR conditions in low cloud ceilings and showers expected from later this afternoon into Tuesday.
Surface winds will continue to blow from a more easterly direction for most areas with stronger wind gusts near heavy rain shower bands and thunderstorms forecast through Monday night.
Tropical Storm force winds are possible near Niihau and Kauai from Monday into Tuesday. Heavy weather MVFR/IFR conditions and wind impacts for these western islands in Kauai County will depend on subtle deviations in the northward track of Hurricane Lowell. Please closely monitor weather conditions for this time period as weather impacts are likely to evolve over time as Lowell continues its northward journey.
AIRMET Sierra for mountain obscuration continues for Kauai Oahu Molokai Maui and the Big Island for the foreseeable future.

Marine

A surface high north of the Hawaiian Islands will persist through the week. Meanwhile, Hurricane Lowell is around 510 nm south- southwest of Kauai, now tracking north-northwest. Lowell will continue to turn toward the north today and as it approaches the island chain winds will begin to increase. Therefore, a Small Craft Advisory (SCA) is now in effect for the typical windy waters and channels around the Big Island and Maui County. Winds will increasingly veer to the southeast to south as Lowell continues to approach, bringing the strongest winds to the western end of the state. Winds and seas will likely exceed small craft criteria across all coastal waters on Monday, which will necessitate an expansion of the SCA. Where winds are expected to be strongest around Kauai County, a Tropical Storm Warning is in effect.
Hurricane conditions are expected in the offshore waters west of 159W Sunday night through Tuesday as the center of the hurricane tracks across the island chain near Nihoa. While confidence is increasing in the track forecast of the cyclone, any slight deviation in the track to the west or east from the current predicted path will have significant differences in impact for the coastal waters around Kauai County. As for Tropical Storm Karina, it is expected to weaken and dissipate as it moves northeast of the state.
Southerly swell generated by Hurricane Lowell will keep surf along south facing shores at High Surf Advisory criteria through at least Monday night. As Lowell begins to turn more north, its swell will gradually veer from south to southwest and begin a rapid upward trend by Monday. Very large surf exceeding warning criteria is likely for south and west facing shores of Oahu and Kauai, and surf may also reach warning levels for the west facing shores of the Big Island, including the Kohala coast on Monday. Coinciding also with monthly high tides, this will create the potential for impacts to harbor entrances, channels, as well as vulnerable coastal properties and infrastructure including roadways. Surf will then rapidly decrease on Tuesday after the hurricane passes north of the island chain. A pulse of northwesterly swell could then bring a minor bump to north shore surf on Tuesday and fade through Thursday.
East facing shores will see continued advisory level surf from a large, medium-period east swell generated by Tropical Storm Karina to the east of the islands. This swell will gradually fade early this week as Karina weakens. Late next week, surf along east facing shores could be bolstered by some medium-period swell generated by Hurricane Marie in the East Pacific. Otherwise, expect choppy conditions from easterly trade wind swell through the week.

Fire weather

Fire weather risk will remain low through the forecast period due to increasing moisture associated with Hurricane Lowell. The temperatures inversion heights are currently near 11,000 ft from Maui to the Big Island, and are expected to remain elevated during the next few days.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Tuesday for Big Island East, Big Island North, Big Island South, Big Island Southeast, East Honolulu, Ewa Plain, Honolulu Metro, Kahoolawe, Kauai East, Kauai South, Kauai Southwest, Kipahulu, Kona, Koolau Windward, Lanai Leeward, Lanai South, Maui Central Valley South, Maui Leeward West, Molokai Leeward South, Molokai Southeast, Molokai West, Molokai Windward, Niihau, Olomana, South Haleakala, South Maui/Upcountry, Waianae Coast, Windward Haleakala.
Tropical Storm Warning for Kauai East, Kauai Mountains, Kauai North, Kauai South, Kauai Southwest, Niihau.
Flood Watch from noon HST today through Tuesday afternoon for Big Island East, Big Island Interior, Big Island North, Big Island South, Big Island Southeast, Big Island Summits, Central Oahu, East Honolulu, Ewa Plain, Haleakala Summit, Honolulu Metro, Kahoolawe, Kauai East, Kauai Mountains, Kauai North, Kauai South, Kauai Southwest, Kipahulu, Kohala, Kona, Koolau Leeward, Koolau Windward, Lanai Leeward, Lanai Mauka, Lanai South, Lanai Windward, Maui Central Valley North, Maui Central Valley South, Maui Leeward West, Maui Windward West, Molokai Leeward South, Molokai North, Molokai Southeast, Molokai West, Molokai Windward, Niihau, Oahu North Shore, Olomana, South Haleakala, South Maui/Upcountry, Waianae Coast, Waianae Mountains, Windward Haleakala.
Tropical Storm Warning for Kauai Channel, Kauai Leeward Waters, Kauai Northwest Waters, Kauai Windward Waters.
Small Craft Advisory until 6 PM HST Monday for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters, Maalaea Bay, Pailolo Channel.

Data Courtesy of NOAA.gov