Iselle becomes a Category 4 hurricane as it closes in on Hawaii

USPA News - Hurricane Iselle unexpectedly strengthened into a major category four hurricane over the Pacific Ocean on early Monday, and computer models still expect the tropical cyclone will hit the Hawaiian islands later this week as a tropical storm, U.S. forecasters said. Iselle continued to strengthen rapidly overnight, reaching category four status on the five-step Saffir-Simpson scale of intensity with maximum sustained winds near 140 miles (220 kilometers), according to an update from the U.S. National Hurricane Center (NHC).

Forecasters had previously expected Iselle to start weakening on Monday morning. "Iselle continues to intensify and has reached category 4 strength," said NHC hurricane specialist Robbie Berg. "Since Iselle has some characteristics of an annular hurricane, it is likely to change little in intensity during the next day or so, and even when it begins to weaken, the trend should be gradual." Iselle is expected to experience an increase in vertical shear and move over colder waters on Wednesday, which should induce quicker weakening at that time. Forecasters now expect Iselle to weaken to a Category 2 hurricane on Tuesday and lose hurricane status by early Thursday as it nears the Hawaiian islands. "Significantly less favorable thermodynamic factors, such as increasingly drier and more stable air and water temperatures just below 26 degrees Celsius (78.8 degrees Fahrenheit), should result in weakening while Iselle nears the Hawaiian Islands," said NHC hurricane specialist Todd Kimberlain. "An accelerated weakening may take place as Iselle makes its closest approach to the Hawaiian chain when environmental conditions become even more hostile." Updated computer models continue to put Iselle`s expected path through the Hawaiian islands, though the forecast cone has moved slightly north when compared to Sunday`s forecast. This change would spare the Big Island the brunt of the storm, but Iselle is still forecast to make landfall on Friday on the other islands. No tropical storm watches or warnings were in effect on Monday, but a tropical storm watch could be issued for the Hawaiian islands as early as Tuesday evening if the forecast does not change. Tropical storms and hurricanes are relatively uncommon for the Hawaiian islands, although a weak Tropical Storm Flossie affected Hawaii in July 2013, causing only minor damage. The last time a tropical cyclone caused casualties in Hawaii was in 1992 when major Category 4 Hurricane Iniki made landfall there, killing six people. Iselle is the ninth tropical cyclone of the Eastern Pacific hurricane season, which officially began on May 15. According to figures released in May, NOAA`s Climate Prediction Center is expecting an above-normal season in the Eastern Pacific basin this year. The outlook calls for 14 to 20 named storms, with 7 to 11 becoming hurricanes and 3 to 6 of them expected to become a major hurricane (category 3 or higher). An average Eastern Pacific hurricane season produces 15 to 16 named storms, with eight to nine becoming hurricanes and four becoming major hurricanes. The Eastern Pacific hurricane season runs from May 15 through November 30, with peak activity from July through September.