By: Civicane49 , 11:09 PM GMT on July 27, 2013
Tropical Storm Flossie is gradually weakening over the central Pacific. As of the 11 am HST advisory from the Central Pacific Hurricane Center (CPHC), the tropical storm has maximum sustained winds at 50 mph and minimum barometric pressure of 1000 mb. It is centered about 915 miles east of Hilo, Hawaii or about 1100 miles east-southeast of Honolulu, Hawaii. The system is moving west-northwestward at 18 mph. Satellite and microwave imagery reveal a weakening tropical cyclone, with the southern half of the thunderstorm activity dissipated and a partially exposed low-level center. Marginal sea surface temperatures at 25-26°C and mid-level dry air have caused the cyclone to weaken during the past several hours and both will continue to play that role during the next few days.
Forecast for Flossie
Flossie will continue to move west-northwestward during the next day or so as it will remain in the southern periphery of a subtropical ridge. As that ridge retrogrades, the cyclone should slowly turn towards the west and slow its forward speed by tomorrow. Forecast models show the cyclone near the Big Island of Hawaii by Monday morning. It should be noted that if Flossie makes landfall on Hawaii as a tropical cyclone, it will be first time to do so since Eugene in 1993.
Flossie will continue the slow weakening trend during the next several days as it will remain in marginal sea surface temperatures and dry, stable atmosphere. Although water temperatures will increase at about 150°W, models are forecasting the southwesterly shear to increase and should result in additional weakening. I strongly believe that Flossie will weaken into a tropical depression on Monday when it is nears the Big Island of Hawaii. The cyclone should dissipate by Tuesday evening after it passes the Hawaiian Islands.
Interests in the Hawaiian Islands should continue to monitor the progress of this storm as it will likely bring locally heavy rain, strong gusty winds, and high surf. It is important to note that weak tropical cyclones, such as a tropical depression, could still bring very heavy rainfall and lead to dangerous flash floods. Since tropical storm conditions are possible by Monday afternoon, tropical storm watches may be required for the Big Island and Maui County by later today.
Figure 1. GOES West visible satellite image of Tropical Storm Flossie to the east of Hawaii. Image credit: NASA/MSFC.
Elsewhere in the tropics
In the Atlantic, Tropical Storm Dorian has succumbed to the hostile environment and degenerated into an open tropical wave. Based on the 1330z ASCAT pass and satellite image, it lacked a closed circulation center. Thus, it no longer meets the criteria of a tropical cyclone. The remnants of Dorian will continue to move generally westward for the next several days and remain north of the Leeward Islands and Puerto Rico. Redevelopment is unlikely to occur as conditions will not be favorable with mid-level dry air and southwesterly shear.
Just off the United States east coast, there is a small, defined area of low pressure, which is designated as “Invest 90L”. Although thunderstorm activity has increased in coverage and intensity during the past few hours, development is unlikely to occur as it will move into cold waters by tomorrow. The system is forecast to move north-northeast during the next few days and will not threaten any land.
I will have an update by tomorrow.
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