Photo Credit: James Grenz

Hilo

Today: Showers and isolated thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 77 near the shore to around 64 at 4000 feet. South winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Cloudy with showers. Locally heavy rainfall possible. Lows 64 to 71 near the shore to around 58 at 4000 feet. South winds up to 15 mph. Chance of rain 90 percent.

Tuesday: Mostly cloudy with scattered showers. Locally heavy rainfall possible. Highs 78 to 83 near the shore to around 67 at 4000 feet. Southeast winds 10 to 15 mph. Chance of rain 50 percent.

Kona

Today: Breezy. Showers and isolated thunderstorms early in the morning, then showers likely and isolated thunderstorms in the late morning and afternoon. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 76 to 84 near the shore to around 64 near 5000 feet. Southeast winds 10 to 20 mph becoming northwest up to 10 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy with scattered showers. Locally heavy rainfall possible. Lows around 72 near the shore to 50 to 58 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tuesday: Mostly cloudy with isolated showers. Locally heavy rainfall possible. Highs 82 to 87 near the shore to around 68 near 5000 feet. Northeast winds up to 10 mph shifting to the south in the afternoon. Chance of rain 20 percent.

Waimea

Today: Showers and isolated thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 75 near the shore to around 68 near 3000 feet. Southeast winds around 10 mph in the morning becoming light. Chance of rain near 100 percent.

Tonight: Mostly cloudy with showers likely. Locally heavy rainfall possible. Lows around 65 near the shore to 56 to 63 near 3000 feet. Light winds becoming southwest up to 10 mph after midnight. Chance of rain 70 percent.

Tuesday: Mostly cloudy with scattered showers. Locally heavy rainfall possible. Highs 65 to 83. Southeast winds up to 10 mph. Chance of rain 40 percent.

Kohala

Today: Showers and isolated thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 75 near the shore to around 68 near 3000 feet. Southeast winds around 10 mph in the morning becoming light. Chance of rain near 100 percent.

Tonight: Mostly cloudy with showers likely. Locally heavy rainfall possible. Lows around 65 near the shore to 56 to 63 near 3000 feet. Light winds becoming southwest up to 10 mph after midnight. Chance of rain 70 percent.

Tuesday: Mostly cloudy with scattered showers. Locally heavy rainfall possible. Highs 65 to 83. Southeast winds up to 10 mph. Chance of rain 40 percent.

South Big Island

Today: Breezy. Showers and isolated thunderstorms early in the morning, then showers likely and isolated thunderstorms in the late morning and afternoon. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 79 near the shore to around 63 near 5000 feet. East winds 15 to 20 mph increasing to around 25 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Locally heavy rainfall possible. Lows around 72 near the shore to around 54 near 5000 feet. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tuesday: Breezy. Mostly cloudy with isolated showers. Locally heavy rainfall possible. Highs around 82 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Today: Showers and isolated thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 77 near the shore to around 64 at 4000 feet. South winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Cloudy with showers. Locally heavy rainfall possible. Lows 64 to 71 near the shore to around 58 at 4000 feet. South winds up to 15 mph. Chance of rain 90 percent.

Tuesday: Mostly cloudy with scattered showers. Locally heavy rainfall possible. Highs 78 to 83 near the shore to around 67 at 4000 feet. Southeast winds 10 to 15 mph. Chance of rain 50 percent.

Waikoloa

Today: Showers and isolated thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 75 to 82 near the shore to 61 to 67 above 4000 feet. Light winds. Chance of rain near 100 percent.

Tonight: Mostly cloudy with scattered showers. Locally heavy rainfall possible. Lows 69 to 75 near the shore to 51 to 56 above 4000 feet. Light winds. Chance of rain 50 percent.

Tuesday: Mostly cloudy with isolated showers. Locally heavy rainfall possible. Highs 82 to 87 near the shore to 66 to 71 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A kona low will linger just west northwest of Kauai this morning drifting slowly westward through Wednesday. A large band of heavy rain associated with this low will also track slowly westward across the state. Expect widespread heavy rainfall with this system, especially under the large heavy rain band, capable of producing catastrophic flooding, and strong gusty southerly winds through Wednesday. The heaviest rainfall currently over Maui County this morning will slowly drift westward into Oahu and Kauai later this morning. Improving weather conditions will start over the eastern side of the state by late Tuesday with drier air slowly spreading into the western islands on Wednesday. More typical trade wind weather will return from late Wednesday onward.

Discussion

This mornings satellite imagery shows a kona low roughly 300 to 400 miles west of the island of Kauai with a large plume of clouds around 300 miles wide extending from Kauai eastward to the Big Island. Deep convective showers continue to develop within this tropical moisture plume producing widespread rain, heavy at times, across the island chain. Radar imagery this morning shows bands of moderate to heavy showers developing and moving northward in the southerly winds. Strong and gusty winds are also observed in the 20 to 35 mph range with gusts up to 50 mph in some areas. The latest rainfall observations in Maui County show from 2 to 10 inches of rain has fallen over the past 24 hours with more rainfall expected today and tomorrow.
The main threats with this kona low will be continued widespread heavy rain and strong southerly winds. Widespread storm total rainfall amounts in the 10 to 15 inch range are forecast with isolated areas of 20 to 25 inches of rainfall. Rain events of this magnitude can produce catastrophic flooding and affect areas that are typically drier, such as the south and west slopes of each island. Isolated thunderstorms also remain in the forecast into Wednesday.
Some additional impacts include dangerous driving conditions due to near zero visibility. Many roads could become impassable due to severe runoff and flooding. Numerous land slides are also expected in areas with steep terrain. Debris in streams and gulches may clog bridges and culverts resulting in dangerous flooding. Urban areas, especially on Oahu, could have severe flooding. Isolated highways, such as the Belt Highway in the Big Island’s Kau District, and Piilani Highway on Maui, may be closed in one or more locations, resulting in long detours or even the isolation of some communities.
Strong and gusty south to southwest winds will continue today. Wind Advisories remain in effect for all Hawaiian Islands including the summits areas of Maui and Hawaii Counties. These strong southerly winds may produce damaging downslope winds over areas along the northern slopes of mountain ranges. Oahu and portions of Molokai may be especially vulnerable to these downsloping gusty winds.
A Winter Weather Advisory was issued this morning for the summits of Mauna Kea and Mauna Loa on the Big Island above 12,000 feet elevation and will remain in effect through 6 PM HST.
Weather conditions are forecast to improve from east to west starting on Wednesday, as the kona low drifts further westward away from the main Hawaiian Islands. Higher pressure will build in north of the state allowing an easterly trade wind weather pattern to return with more typical passing windward and mountain showers.

Aviation

Early this morning, a kona low located west northwest of Kauai is resulting in southerly flow across the island chain. Latest satellite and radar imagery show bands of showers, some of which are producing heavy rain, streaming across the island chain from the Kauai Channel to the Big Island. MVFR conditions are widespread across the state with IFR and even some LIFR visibilities and ceilings observed within the heaviest showers.
As the axis of heaviest showers continues to slowly drift westward this morning, periodic breaks are likely across Maui County before additional showers develop later this morning and this afternoon. Regardless, there will be numerous impacts for aviation interests throughout the forecast period and beyond including frequent MVFR conditions with periods of IFR and LIFR. Winds will be rather strong as well in some locations, with gusts in excess of 40kts possible. While isolated thunderstorms remain possible throughout the period, the main threat will be heavy rainfall that will result in low visibility and ceilings.
Numerous AIRMETs remain in effect this morning. AIRMET Sierra has been issued for tempo IFR conditions across Maui, Lanai, Molokai, Oahu, and portions of the Big Island. Additionally, tempo mountain obscuration AIRMETs remain in effect for the rest of the Big Island and Kauai, though these may need to be adjusted later this morning based on latest satellite trends. AIRMET Sierra for mountain obscuration and/or IFR conditions are expected to continue over the next two days.
In addition, AIRMET Tango remains in effect north and east of the mountains of all major Hawaiian Islands for mechanical low-level turbulence. For now, AIRMET Tango also remains in effect for sustained wind speeds greater than 30kts statewide, though wind speeds have started to diminish across the Big Island early this morning.

Marine

A slow-moving kona low located about 300 nm west northwest of Kauai is producing a large convergence bands of heavy rain, with an occasional isolated thunderstorm, across most local waters. These moderate to strong bands of rain, in tandem with the wind acceleration around Mauna Kea, Mauna Loa and Haleakala, have produced strong winds frequently gusting to gale force as verified by a late Sunday evening ASCAT-C pass. As the low moves westward the next several days, convergence bands of precipitation will generally spread more westward over Oahu today and eventually in the proximity of Kauai later today or early Tuesday. Bands of primarily showers with isolated storms will likely linger over the western end of the island chain Tuesday and then move west of the islands Wednesday as high pressure building in northeast of the state reinstates a moderate to fresh trade wind regime.
To account for strong rain convergent bands passing across more western islands today, a Gale Warning is now in in effect for the coastal waters west of the Kaiwi Channel including the channel. A Small Craft Advisory (SCA) is in effect for the remaining eastern Hawaiian nearshore waters due to a combination of these high winds and seas that still remain elevated due to the passage of a large north swell. The greatest potential for the strongest maritime winds the next few days will be within any band of showers that may or may not contain embedded thunderstorms. Strengthening trade winds will maintain SCA conditions, especially for those typically windier waters around Maui and Big Island Tuesday night or Wednesday.
The most recent swell observations at the far northwest offshore buoys are beginning to show that the large north swell that peaked yesterday has begun a slow and steady decline. Swell at both offshore NOAA 001 and 101 buoys are observing a near 10 foot, 12-14 second swell (versus near 20 feet, 15 seconds a mere 24 hours ago). Surf has fallen below High Surf Warning heights and therefore have lowered flags to a High Surf Advisory (HSA) that is in effect for all north facing shorelines through the day. The HSA for west facing shores has been allowed to expire as surf heights have fallen below 12 feet (8 feet Big Island). North shore surf will likely fall below HSA levels tonight and will fade to small heights from late Tuesday into the weekend. Strong southerly winds within and near recently strong convergent overnight rain bands developing far east of a kona low northwest of Kauai have produced periods of rough, short period chop that will be impacting south facing shores today. The latest PacIOOS buoy at Pearl Harbor has shown a very significant spike in significant wave heights from 3 feet a few hours ago to near 10 feet at 0300 HST. As high pressure builds in from the northeast later this week, strengthening trade winds will result in elevated rough wind wave surf along most east facing shores from mid week onward. By Wednesday, increasing trade winds will produce elevated rough wind wave surf along most east facing shores.
Abnormally high ocean levels are coinciding with seasonal peak high tides the next couple of days. Although the north swell is declining, some elevated coastal run up may occur at peak high tide times early this morning. Even in areas not affected by swell, ocean levels will be elevated and some coastal inundation may occur, especially during periods of heavy rainfall. (Urban) flooding such as what was experienced in the Waikiki area yesterday has prompted a Coastal Flood Statement to primarily increase potential nuisance flooding awareness during high tides.

HFO Watches/Warnings/Advisories

Flood Watch through Tuesday afternoon for all Hawaiian Islands.
High Surf Advisory until 6 PM HST this evening for north facing shores of all islands.
Wind Advisory until 6 PM HST this evening for all Hawaii Islands.
Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for all Maui County and Big Island waters.
Gale Warning until 6 PM HST this evening for all Kauai and Oahu waters including the Kaiwi Channel.

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Data Courtesy of NOAA.gov