Downgraded Storm Flossie Leaving Hawaii: AIR Worldwide

July 30, 2013

According to catastrophe modeling firm AIR Worldwide, the remnants of what was Tropical Storm Flossie are currently northwest of Kauai, the northernmost main island of the Hawaiian chain of islands, moving west-northwest away from the islands at about 15 miles per hour. According to a public advisory by the Central Pacific Hurricane Center, Flossie’s maximum sustained winds have weakened to 30 mph.

“Yesterday Flossie was a tropical storm with maximum winds of 45 to 50 mph when it passed within about 20 miles of the southernmost Big Island and then past Maui, the next island to the northwest,” said Scott Stransky, senior scientist at AIR Worldwide. “It was the first direct tropical storm impact on Hawaii in 21 years, since Hurricane Iniki struck Kauai and caused considerable damage in 1992. However, as Flossie approached Big Island it encountered upper atmosphere wind shear that weakened it; continued shear and interaction with the mountains on the Big Island and Maui weakened it further.”

In public advisory yesterday, the Central Pacific Hurricane Center downgraded Flossie to a tropical depression, and this morning, in its 5:00 a.m. HST (11:00 a.m. EDT) advisory, the Center downgraded the storm further to a Post-Tropical Remnant Low.

Flossie first came to the attention of the National Hurricane Center (NHC) in Miami as an area of low pressure off the coast of Mexico. Three days later it was upgraded to a tropical depression, then to a tropical storm. On July 27 Flossie crossed from the NHC’s area of responsibility to that of the Central Pacific Hurricane Center.

Stransky noted, “Storms that approach the Hawaiian Islands from the south, such as Iniki, tend to be stronger than a Flossie-like storm approaching from the east, since they spend more time over warmer sea surface regions. Flossie, however, helps confirm the scientific understanding that all of the Hawaiian Islands are at risk from tropical storms.”

According to AIR, at Flossie’s wind speeds, the chief exposures at risk were residential buildings. Most single-family and duplex homes in Hawaii are of wood frame construction, about 40 percent of which are only single wall wood frame. These structures have load-bearing walls generally made of thin plywood boards, and have greater susceptibility to wind damage. They fared poorly when Hurricane Iniki struck. Because of this susceptibility and the additional concern over possible heavy rainfall—initially as much as 12 inches was forecast for some locations—on Sunday the Governor of Hawaii issued a declaration of emergency.

Flossie weakened as it approached the islands, however, and never made actual landfall. According to reports, its impact has been relatively mild. Strong, gusty winds knocked out electricity to about 10,000 customers, mainly on Maui and the Big Island. Streetlights and other public services such as running water also were intermittently affected in some places. All airports remained open, but many flights were canceled or delayed ahead of the storm’s arrival.

By late Monday there were no reports of serious damage in the Maui County group of islands. However, many trails, campsites, and some roads in mountainous parts of the islands remain closed, and a flash flood watch is in place throughout the islands through Wednesday morning in anticipation of possible flooding or mud slides.

Stransky concluded, “A threat of high surf remained throughout the day yesterday and into this morning along eastern shores, with swells peaking yesterday afternoon. The Big Island received surf as high as 16 feet, and Maui was expected to see waves as high as 12 to 18 feet.”

According to the Central Pacific Hurricane Center, Post-Tropical Cyclone Remnant Flossie is now moving into a somewhat less hostile environment. The Center reported that satellite data and surface observations show no organized thunderstorm activity nor indications of a well-defined center of circulation, and has declared Flossie to no longer be a tropical cyclone. The Center is forecasting that Flossie will remain a remnant low for some time before dissipating as it continues to track into the open Pacific.

AIR is also monitoring the remnants of Tropical Storm Dorian in the Atlantic, currently passing through the Turks and Caicos Islands, and the newly formed Tropical Depression 7 (likely to be named “Gil” shortly) in the Eastern Pacific, which has formed near where Flossie formed, well off the coast of Mexico.

Source: AIR Worldwide

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