UPDATE: High surf warning issued as Tropical Storm Calvin nears the Big Island

Update at 5:46 p.m. July 18: The National Weather Service forecast office in Honolulu has issued a high surf warning for the east-facing shores of Kauaʻi through 6 p.m. Wednesday, courtesy of Tropical Storm Calvin, which is forecast to pass just south of the Big Island before moving off to the west of the state later this week.

Calvin will rapidly generate warning level surf tonight into Wednesday morning for exposed east-facing shores of the Big Island and most of Maui County, then quickly subside through the rest of Wednesday as the storm moves farther west away from the Big Island. Surf will build tonight into early Wednesday morning for east-facing shores of Kauaʻi, generating advisory level surf through Wednesday before lowering into Thursday morning.

Strong breaking waves and strong currents will make swimming dangerous throughout the advisory period.

Kauaʻi and Niʻihau also remain under a flood watch through Wednesday afternoon.

Original story: Tropical Storm Calvin is expected to pass well south of Kauaʻi, but it will produce periods of heavy rainfall over the island that could lead to flooding and landslides over steep terrain, especially over windward mountain slopes.

The National Weather Service issued a flood watch for Kauaʻi, Oʻahu and Niʻihau.

Tropical Storm Calvin is expected to begin impacting the Big island tonight, with rainfall of 4 to 8 inches and possibly 10 inches mainly on the windward areas. Hawaiʻi County could experience flash flooding and mudslides.

As of 5 a.m. Tuesday, Calvin was 390 miles east-southeast from Hilo and moving at 22 mph toward the Big Island with maximum sustained winds of 45 mph and higher gusts, according to the National Hurricane Center.

The storm is expected to pass over, or just south of the Big Island tonight through Wednesday night — and south of the Hawaiian Islands.

This places the islands in the windier and wetter part of Calvin’s circulation. Tropical-storm-force winds extend outward up to 105 miles from the center.

North winds will shift to the northeast and east as Calvin moves westward through Wednesday morning. Winds will primarily be northeasterly over the smaller islands, strongest Wednesday and Wednesday night. It is important to note that the mountainous terrain of the islands can produce localized areas of enhanced winds, even well away from the tropical cyclone center.

Calvin will bring rapidly building surf tonight through Wednesday. Surf may reach as high as 15 feet along east-facing shores of the Big Island, and up to 10 feet along east-facing shores of the other islands. Although peak surf heights on the Big Island will likely occur around low tide Wednesday morning, some minor overwash and erosion is possible for exposed low-lying
coastal areas.

Deep convection has been developing near Calvin Tuesday morning, which may slow the weakening trend today. Calvin is forecast to gradually weaken from tonight through Thursday.

Residents and visitors should complete any last minute preparations today during the daylight hours before the storm strikes. For information about how to get ready, click here.

Swells generated by Calvin are expected to begin spreading across the main Hawaiian Islands later today and tonight. This will lead to a rapid increase in surf along east facing shores,
with high surf continuing into Wednesday. This elevated surf will likely cause life-threatening conditions along exposed shorelines.

Potential Impacts:

Wind: Protect against hazardous wind having possible limited impacts across the Hawaiian islands. Potential impacts include:

• Damage to porches, awnings, carports, sheds, and unanchore mobile homes. Unsecured lightweight objects blown about.
• Many large tree limbs broken off. A few trees snapped or uprooted, but with greater numbers in places where trees are shallow rooted. Some fences and roadway signs blown over.
• A few roads impassable from debris, particularly within urban or heavily wooded places. Hazardous driving conditions on bridges and other elevated roadways.
• Scattered power and communications outages.

Surge: Protect against locally hazardous surge having possible limited impacts across portions of windward and southeast Big Island. Potential impacts in this area include:

• Localized inundation with storm surge flooding mainly along immediate shorelines and in low-lying spots, or in areas farther inland near where higher surge waters move ashore.
• Sections of near-shore roads and parking lots become overspread with surge water.
• Driving conditions dangerous in places where surge water covers the road.
• Moderate beach erosion. Heavy surf also breaching dunes, mainly in usually vulnerable locations. Strong rip currents.
• Minor to locally moderate damage to marinas, docks, boardwalks and piers. A few small craft broken away from moorings.

Elsewhere across the Hawaiian islands, little to no impact is anticipated.

Flooding raing: Protect against dangerous rainfall flooding having possible significant impacts across mainly windward and southeastern portions of the Big Island. Potential impacts include:

• Moderate rainfall flooding may prompt several evacuations and rescues.
• Rivers and tributaries may quickly become swollen with swifter currents and overspill their banks in a few places, especially in usually vulnerable spots. Small streams, creeks, canals, arroyos, and ditches overflow.
• Flood waters can enter some structures or weaken foundations.
• Several places may experience expanded areas of rapid inundation at underpasses, low-lying spots, and poor drainage areas. Some streets and parking lots take on moving water as storm drains and retention ponds overflow.
• Driving conditions become hazardous. Some road and bridge closures.

Prepare for locally hazardous rainfall flooding having possible
limited impacts across other Hawaiian Islands from Kaua’i to Maui.

Tornadoes: Protect against a tornado event having possible limited impacts
across the Hawaiian islands. Potential impacts include:

• The occurrence of isolated tornadoes can hinder the execution of emergency plans during tropical events.
• A few places may experience tornado damage, along with power and communications disruptions.
• Locations could realize roofs peeled off buildings, chimneys toppled, mobile homes pushed off foundations or overturned, large tree tops and branches snapped off, shallow-rooted trees knocked over, moving vehicles blown off roads, and small boats pulled from moorings.