Hilo

Today: Tropical storm conditions expected. Showers and isolated thunderstorms until late afternoon, then numerous showers late in the afternoon. Locally heavy rainfall possible. Highs 80 to 87 near the shore to 66 to 71 at 4000 feet. Southeast winds 10 to 40 mph with gusts to 70 mph decreasing to 10 to 20 mph with gusts to 50 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy with numerous showers in the evening, then partly cloudy with scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 65 to 74 near the shore to around 60 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Thursday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 86 near the shore to 66 to 73 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Kona

Today: Tropical storm conditions expected. Mostly cloudy. Numerous showers in the morning. Isolated thunderstorms until late afternoon. Scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 86 to 91 near the shore to around 75 near 5000 feet. Southeast winds up to 40 mph with gusts to 70 mph shifting to the northeast up to 30 mph with gusts to 60 mph in the afternoon. Chance of rain 70 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows around 75 near the shore to 55 to 60 near 5000 feet. North winds up to 20 mph with gusts to 45 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny. Scattered showers in the afternoon. Highs 85 to 90 near the shore to around 73 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Waimea

Today: Tropical storm conditions expected. Showers in the morning. Isolated thunderstorms through the day. Numerous showers in the afternoon. Locally heavy rainfall possible until late afternoon. Highs around 82 near the shore to 72 to 81 near 3000 feet. East winds up to 45 mph with gusts to 70 mph becoming northeast up to 20 mph with gusts to 45 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 66 to 74 near the shore to 59 to 65 near 3000 feet. East winds up to 25 mph with gusts to 50 mph. Chance of rain 50 percent.

Thursday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 65 to 86. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Kohala

Today: Tropical storm conditions expected. Showers in the morning. Isolated thunderstorms through the day. Numerous showers in the afternoon. Locally heavy rainfall possible until late afternoon. Highs around 82 near the shore to 72 to 81 near 3000 feet. East winds up to 45 mph with gusts to 70 mph becoming northeast up to 20 mph with gusts to 45 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 66 to 74 near the shore to 59 to 65 near 3000 feet. East winds up to 25 mph with gusts to 50 mph. Chance of rain 50 percent.

Thursday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 65 to 86. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

South Big Island

Today: Tropical storm conditions possible. Showers and isolated thunderstorms until late afternoon, then scattered showers late in the afternoon. Locally heavy rainfall possible in the morning. Highs around 85 near the shore to 67 to 72 near 5000 feet. East winds 15 to 35 mph with gusts to 55 mph. Chance of rain near 100 percent.

Tonight: Mostly clear. Windy. Isolated showers in the evening. Lows around 75 near the shore to around 56 near 5000 feet. Northeast winds up to 30 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

Thursday: Mostly sunny. Breezy. Highs around 86 near the shore to around 69 near 5000 feet. East winds up to 25 mph.

Puna

Today: Tropical storm conditions expected. Showers and isolated thunderstorms until late afternoon, then numerous showers late in the afternoon. Locally heavy rainfall possible. Highs 80 to 87 near the shore to 66 to 71 at 4000 feet. Southeast winds 10 to 40 mph with gusts to 70 mph decreasing to 10 to 20 mph with gusts to 50 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy with numerous showers in the evening, then partly cloudy with scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 65 to 74 near the shore to around 60 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Thursday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 86 near the shore to 66 to 73 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Waikoloa

Today: Tropical storm conditions expected. Mostly cloudy. Numerous showers early in the morning. Isolated thunderstorms until late afternoon. Scattered showers in the late morning and afternoon. Locally heavy rainfall possible early in the morning. Highs 85 to 91 near the shore to 70 to 76 above 4000 feet. East winds up to 45 mph with gusts to 70 mph becoming north up to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly clear. Breezy. Isolated showers in the evening. Lows around 76 near the shore to 55 to 60 above 4000 feet. Northeast winds up to 25 mph shifting to the southeast after midnight. Gusts up to 45 mph. Chance of rain 20 percent.

Thursday: Sunny and windy. Highs 85 to 91 near the shore to 70 to 77 above 4000 feet. Northeast winds up to 30 mph.

Detailed Forecast

Synopsis

Strong winds and rainfall activity will spread across the state today as Tropical Storm Calvin moves swiftly westward passing south of the smaller islands. Tropical Storm impacts may occur far north of the storm center with wind, rain and water impacts affecting all islands in the state. Strong damaging winds remain in the forecast for portions of Hawaii and Maui Counties. Expect heavy showers and flash flooding in some areas with the greatest threat of flash flooding forecast over east and southeast slopes of the Big Island and windward Maui through the morning hours. Calvin will quickly pass west of the Hawaiian Islands on Thursday as it weakens into a Tropical Depression. Breezy trade wind weather with decreasing shower coverage will fill in rapidly as Calvin departs the region from Thursday onward.

Discussion

Tropical Storm Calvin continues to move on a high confidence westerly track passing near the Big Island tonight and south of the rest of the Hawaiian Islands today. Tropical Storm impacts may develop far north of the center of this storm. The most damaging wind and weather conditions are currently focused over the Big Island and the islands in Maui County through at least the morning hours. The strongest gusts will develop over and downwind of island mountains and ridges. Power outages and downed trees will be possible. Due to the rapid speed of Calvin, weather conditions will quickly change with potentially hazardous weather conditions spreading westward down the island chain today. Each island will only see a period of around 12 to 18 hours of weather impacts from Calvin due to the fast motion of this storm.
Big Island Impacts… Strong damaging Tropical Storm Force winds and heavy rainfall leading to flash flooding are likely with this storm. Rainfall rates of 3 inches per hour will develop in some areas, increasing the threat of flash flooding and rock/mud slides through at least this morning. Over the past 12 hours 3 to 5 inches of rain has fallen over eastern slopes of the Big Island, and an additional 2 to 4 inches are possible as Calvin moves away from the island. The greatest rainfall and flood threats will likely occur near Hilo, and over the Puna and Kau Districts. The greatest wind accelerations are expected over areas around and downwind of terrain such as the saddles, South Point and the Kohala districts. Winds this strong will be capable of knocking down trees and causing power outages, so please limit travel if possible until the storm passes. Conditions are expected to quickly improve by this afternoon with high pressure moves in from the east.
Maui County Impacts… Strong easterly winds with unstable tropical moisture will produce periods of heavy rain over the islands in Maui County, especially over the windward mountain slopes. Over the past 12 hours some areas on Maui have reported up to 2 inches of rainfall with this storm, and an additional 2 to 4 inches of rainfall are possible as Calvin passes south of Maui County. A Flood Watch remains in effect through this afternoon. Damaging winds may also develop in some areas of Maui County today with the strongest winds developing over and downwind of island mountains. Wind gusts near 60 mph will be possible and a High Wind Warning remains in effect until this evening. Winds this strong will be capable of knocking down trees and causing power outages, so please limit travel if possible.
Oahu and Kauai County Impacts… A Wind Advisory remains in effect due to gusty east to northeast winds steadily increasing through the day today. The strongest wind gusts will occur over and downwind of island mountains. The potential for heavy showers will also increase today as Calvin passes south of each island. Rainfall totals of 2 to 4 inches are expected for Kauai and Oahu today with the heaviest rain expected over windward mountains. Rain shower bands will move quickly due to the strong winds. Any showers that anchor or train over one location then flash flooding will be possible. A Flood Watch remains in effect through this afternoon. Power outages and downed trees are possible, so please plan accordingly.
By Thursday, Calvin will continue to weaken and pass quickly west of the island chain. High pressure will build in quickly as Calvin exits the region. High pressure will build in behind the passing storm producing more stable breezy trade wind weather with rapidly decreasing shower trends. This trade wind weather will continue through the upcoming weekend with upward trends in shower activity on Saturday and Sunday, mainly over windward and mountain areas.

Aviation

Tropical Storm Calvin is forecast to continue moving west remaining in close proximity to the island chain and will heavily impact the forecast through tonight.
Heavy rain associated with Calvin will continue along the windward coasts and slopes of the Big Island and Maui county with IFR conditions remaining through at least mid morning. Thunderstorms and gusty winds in excess of 40 mph are also possible for that time. Leeward portions of the Big island could still experience strong gusts and heavy showers throughout the day.
For the rest of the islands, strong northeast to easterly winds will prevail across the island chain. Wind gusts in excess of 30 kts have been observed at a couple of area airports. As a result, AIRMET Tango remains in effect for moderate low-level turbulence statewide. This AIRMET will likely remain through the day. Meanwhile, bands of low clouds and showers are starting to move through Oahu and Kauai and will likely increase in coverage and intensity throughout the morning. AIRMET Sierra remains in effect for tempo mountain obscuration for Maui, Molokai, Oahu, and Kauai. Conditions overall should improve later this evening from east to west as Calvin moves west and weakens further, with a more typical trade wind pattern building in later tonight into Thursday.
A Tropical Storm Warning remains in effect for the Big Island and its adjacent waters, a High Wind Warning for Maui County, and Wind Advisories for Oahu and Kauai.
TC SIGMET Romeo will cover portions of the island chain. As a reminder, all aviation hazards are implied within a tropical cyclone SIGMET, including severe turbulence, icing, thunderstorms/lightning, and low-level wind shear. Aviation interests should continue to monitor for the latest forecast updates throughout the day

Marine

Tropical Storm Calvin is currently located around 80 nautical miles from the southern end of the Big Island and is tracking west at 17 knots. Calvin will pass well south of the smaller islands today as it weakens. A Tropical Storm Warning remains in effect for the offshore waters, as well as the Alenuihaha Channel and all waters surrounding the Big Island through this afternoon. The Gale Warning for the Pailolo Channel and Maalaea Bay remains in effect through this afternoon as well. The Small Craft Advisory has been extended elsewhere through tonight as fresh to locally strong easterly winds persists.
Warning level surf generated by Calvin has peaked and will trend down through this afternoon. The High Surf Advisory will continue for east facing shores of Kauai and Oahu through this afternoon, but may need to be extended as the swell propagates north through the island chain. Even though low tide will coincide with the peak surf heights, minor overwash and erosion can occur for exposed low- lying coastal areas, especially through the morning hours. South facing shores will see a slight bump in surf as the fetch from the east side of Calvin generates a small, short period south swell through tonight. Otherwise, no significant swells are expected through the weekend.
A return to a more typical trade wind pattern is expected Thursday through the weekend with moderate to locally strong trades. The SCA will likely continue for typically windy areas around Maui County and the Big Island.

HFO Watches/Warnings/Advisories

Tropical Storm Warning for Big Island.
Tropical Storm Warning for Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
High Wind Warning until 6 PM HST this evening for all islands in Maui County.
Wind Advisory until 6 PM HST this evening for Oahu and Kauai.
Flood Watch through this afternoon for Kauai, Niihau, Oahu, Maui and Hawaii Counties.
Gale Warning until 6 PM HST this evening for Maalaea Bay, Pailolo Channel.
Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters.
High Surf Warning until 6 PM HST this evening for east facing shores of Molokai, Kahoolawe, Maui and the Big Island.
High Surf Advisory until 6 PM HST this evening for east facing shores of Oahu and Kauai.

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Data Courtesy of NOAA.gov