UPDATE No. 6: Calvin now 140 miles south of Hilo; flood advisory issued for eastern portions of Big Island

Update No. 6 at 11 p.m. July 18: Tropical Storm Calvin now is 140 miles south of Hilo, traveling west at 20 mph with maximum sustained winds dropping to 50 mph, but with higher gusts.

Rain has begun to fall in Hilo, with winds picking up.

The eye of Tropical Storm Calvin is being tracked by the South Hawai’i WSR-88D radar as it moves westward toward the waters near South Point on the Big Island. A Hurricane Hunter aircraft, which is currently flying into Calvin, indicates maximum flight level winds of 50 knots.

Update No. 5 at 8 p.m. July 18: Tropical Storm Calvin continues its approach toward the Big Island, with impacts imminent and that will spread over the island. As of 8 p.m., the storm was about 150 miles south-southeast of Hilo and 130 miles southeast of South Point with maximum sustained winds of 60 mph.

Calvin was continuing its westward track, moving at 21 mph. Tropical storm-force winds extend 140 miles out from the storm’s center.

A tropical storm warning remains in effect for Hawaiʻi County until further notice. A flood watch also remains in effect for all Hawaiian islands through 6 p.m. Wednesday and a high surf warning for east-facing shores of the Big Island and Maui is also in effect through 6 p.m. Wednesday.

A flood advisory also has been issued for portions of the Big Island until 11:15 p.m. today because of flooding caused by excessive rainfall from Tropical Storm Calvin.

At 8:05 p.m., radar indicated heavy rain over east sections of the Big Island. Heavy rain was falling at a rate of 1 to 2 inches per hour in some areas and increasing in coverage as Calvin approaches from the east.

Some locations that will experience flooding include Hilo, Hawaiian Paradise Park, Waikōloa Village, Kapa’au, Honokaʻa, Pōhakuloa Camp, Pōhakuloa Training Area, Volcano, Glenwood, Mountain View, Hawaiʻi Volcanoes National Park, Pāpaʻikou, Honomū, Pepeʻekeo, Wood Valley, Keaʻau, Hawaiian Acres, Laupāhoehoe and Hakalau.

The public is advised to stay away from flooded areas including roadways; most flood deaths occur in vehicles. Riverbanks and culverts also can become unstable and unsafe.

Original story: As of 5 p.m. today, Tropical Storm Calvin was approaching the Big Island and was about 175 miles southeast of Hilo and 175 miles east-southeast of South Point, with maximum sustained winds of 60 mph. The storm was continuing a westward track, moving at 21 mph.

A tropical storm warning remains in effect for Hawaiʻi County until further notice. A flood watch also remains in effect for all Hawaiian islands through 6 p.m. Wednesday and a high surf warning for east-facing shores of the Big Island and Maui is also in effect through 6 p.m. Wednesday.

Tropical storm conditions are likely to begin spreading over the Big Island starting this evening. Tropical storm-force winds extend up to 140 miles out from the storm’s center, which is still expected to pass very close to the south portion of the island.

Calvin is forecast to remain a tropical storm throughout the next 36 hours and then weaken quickly.

The storm, which was forecast to weaken as it got closer to the island, was on a strengthening trend earlier in the day thanks to a strong trade wind pattern in place.

“It is little bit of a confusing situation since we had stronger trade winds ahead of the system, so as Calvin advances closer to the islands it’s pinching what we call the pressure gradient, so as you get a tighter pressure gradient, the wind speeds start to accelerate,” said Leigh Anne Eaton, an emergency response specialist with the National Weather Service Pacific Region headquarters in Honolulu, who has been on the Big Island since Tuesday to assist emergency officials.

Eaton said Calvin is pushing against normal winds and speeding them up: “It’s like if you had something in a channel of water, if you make it tighter, then it’s going to speed up.”

Those strong wind speeds will continue into tonight. Winds will transition to those associated with Calvin sometime this evening. The strong winds carry with them the potential for broken and downed tree branches and downed powerlines and power outages.

Heavy rains will also begin tonight.

“You can already start to see on the radar just some very early hints of some of the rainfall starting to come into the Big Island, but we’re really thinking as we get into like 6 p.m. time frame that’s when it’s going to start to pick up a little bit … and then by 8 to 10 p.m. is really when we’re gonna see the heaviest rain start,” Eaton said at about 3 p.m. Tuesday.

Heavy rain and wind will continue for more of the island through the early morning hours Wednesday, with the east side of the island from ʻUpolu Point through Hilo and farther south down to Nāʻālehu getting the brunt of the storm.

As Calvin’s center moves west of the islands, southeast portions of the island could start to see some heavy rainfall, likely after midnight and into the early morning hours.

Some places could see upward of 2 inches of rainfall per hour. Storm total rainfall amounts through Thursday are forecast to be 4 to 8 inches, with maximum amounts of 10 inches possible, mainly along the windward slopes and southeast flank of the Big Island. That heavy rainfall could cause flash flooding and mudslides.

Another main concern is high surf. Swells generated by Calvin are also expected to begin spreading across the main Hawaiian Islands tonight, leading to a rapid increase in surf along east-facing shores. High surf is expected to continue into Wednesday, likely causing life-threatening conditions along exposed shorelines.

Forecasters are not ruling out a chance for the storm’s center to make landfall as there is still some possibility Calvin could wobble to the north. If it does, it would do so likely somewhere in the South Point area, Eaton said, and storm impacts would not change.

Most models continue to show the center still passing close to the island to the south.

“But with that, we don’t really want to focus on that center point so much because with how Calvin is set up right now, we’ve got all of the moisture and all of the energy to the north side of it,” Eaton said. “So really, with the center passing just south of the Big Island, we’re going to push all of that moisture and those stronger winds up through the Big Island.

The storm’s heaviest impacts should last between 10 and 12 hours.

It does not look like Calvin will make any turns to the north and likely will continue on its westerly track and away from the islands. However, as it continues moving west, the deep moisture associated with the storm will spread across the smaller islands. So windward areas of Maui could still experience some heavy rainfall.

Once the storm gets more west of the Big Island, it will start to encounter upper level wind shear that will really start to weaken it, Eaton said, and by Thursday should be in a degraded state.

“Calvin will likely weaken into a tropical depression by Thursday, with breezy trade wind weather returning Thursday through the weekend,” the National Weather Service forecast office in Honolulu said in its 5 p.m. Hawaiʻi area synopsis.

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