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Weakening Flossie nears Hawaii; ex-Dorian remains poorly organized
By: Civicane49, 8:10 PM GMT on July 29, 2013
Tropical Storm Flossie is closing in on Hawaii as it continues to weaken. As of the 8 am HST advisory from the Central Pacific Hurricane Center (CPHC), the tropical storm has maximum sustained winds at 40 mph and minimum barometric pressure of 1000 mb. It is centered about 90 miles northeast of Hilo, Hawaii or about 260 miles east-southeast of Honolulu, Hawaii. The system is moving west-northwestward at 20 mph. Recent satellite image reveals that Flossie is barely a tropical storm, with the low-level circulation center being exposed and the thunderstorm activity shifted to the southeast of the center, thanks to high northwesterly shear and dry air. Radar from the Big Island shows heavy rain remaining just off to the east and should move into the Big Island in the next few hours.
Forecast for Flossie
In response to the re-location of the center far north, the track guidance shifted north and now takes Flossie over Maui by later this afternoon, passing over Oahu during tonight, then over Kauai by tomorrow morning. Flossie will continue to move west-northwestward for the next several days as it remains south of a well-established subtropical ridge. The cyclone will continue on a slow weakening trend during the next few days, and I would not be surprised to see it weaken to a tropical depression before moving inland on Maui. The combination of dry air and strong northwesterly shear should result in additional weakening. The cyclone should dissipate by Wednesday or sooner after it moves away from Hawaii to the west.
Interests in the Hawaiian Islands should continue to monitor the latest on Flossie as it will likely bring very heavy rain, few thunderstorms, strong gusty winds, and large surf through today into Tuesday. Heavy rainfall could trigger dangerous flash flooding and mudslides. Big Island is expected to receive more rainfall later today and will spread to Maui County and Oahu by later that day. Flossie is expected to bring 6-10 inches of rain over Hawaii and Maui counties and 4-8 inches of rain for Oahu and Kauai. The high winds could result in structural damage and power outages. Tropical storm warnings have been issued for the entire state. Dangerously high surf is pounding the east facing shores of the Big Islands and will spread to the rest of the islands today into Tuesday.
Figure 1. Morning visible satellite image of Tropical Storm Flossie just off to the northeast of the Big Island. Image credit: NOAA Environmental Visualization Laboratory.
Remnants of Dorian not better organized
In the Atlantic, the remnants of Dorian located a couple of hundred miles north of Puerto Rico remains poorly organized. There is no evidence of a well-defined circulation center yet based on the recent data from the Air Force reconnaissance mission. However, satellite presentation remains pretty impressive with well-defined upper-level outflow in the northern semicircle. The main impediment to redevelopment is the upper-level trough situated to the west of Dorian as seen on water vapor imagery. Strong upper-level winds associated with this trough are generating moderate southwesterly shear as well as dry air. None of the forecast models anticipate regeneration, with the exception of the HWRF model, which is historically poor in tropical cyclone genesis. Regardless of redevelopment, the remnants of Dorian are forecast to move west-northwestward during the next few days and could bring showers and gusty winds to Turks and Caicos Islands and the Bahamas during tonight through Wednesday.
Figure 2. Visible satellite image of ex-Dorian. Image credit: NASA/MSFC.
Tropical Storm Flossie aiming towards Hawaii
By: Civicane49, 7:49 PM GMT on July 28, 2013
Tropical Storm Flossie continues to take aim at Hawaii. As of the 5 am HST advisory from the Central Pacific Hurricane Center (CPHC), Flossie has maximum sustained winds at 65 mph and minimum barometric pressure of 996 mb. It is located about 535 miles east of Hilo, Hawaii or about 720 miles east of Honolulu, Hawaii. The system is moving westward at 20 mph. Although Flossie has been over cool waters of 25°C (which is below the 26°C threshold needed for tropical storms to sustain), it remains fairly organized as it continues to produce modest amount of thunderstorms in the center as seen on satellite image.
Figure 1. GOES West infrared satellite image of Tropical Storm Flossie approaching towards Hawaii. Image credit: NASA/MSFC.
Forecast for Flossie
Flossie will continue to move generally westward in the next several days as it remains south of a mid-level ridge. Nearly all the track guidance shows Flossie reaching the Big Island and Maui by tomorrow afternoon and passing south of Oahu on Monday night. The GFS and ECMWF have come into better agreement on the timing, which increases confidence in the forecast. Flossie will weaken steadily during the next several days. Although water temperatures will increase in Flossie’s projected path, a large amount of dry air is evident on water vapor imagery. In addition, shear is forecast to slowly increase in the next few days. The combination of dry air and increasing shear should result in gradual weakening. Yesterday, I believe that Flossie will weaken and make landfall in Hawaii as a tropical depression. However, given the storm’s progress and conditions, a rare tropical storm landfall becomes inevitable. The cyclone should dissipate by Wednesday after it passes the Hawaiian Islands.
Interests in the Hawaiian Islands are urged to monitor the progress of this storm as it will likely bring heavy rain, thunderstorms, strong gusty winds, and large surf on early Monday into Tuesday. Torrential rainfall could trigger dangerous flash flooding and mudslides. Heavy rainfall is anticipated for the Big Island by Monday morning and will spread to Maui County and Oahu by later that day. Flossie is expected to bring 6-10” of rain over Hawaii and Maui counties and 4-8” for Oahu. The high winds could result in power outages and some structural damage. Gust could reach up to 60 mph for some localized areas. Tropical storm warnings have been issued for the Hawaii and Maui counties and tropical storm watch is issued for Oahu. Tropical storm watch may be required for the Kauai County by later today. Dangerously high surf will begin to impact the east facing shores of the islands by tonight and is expected to peak on Monday and Tuesday.
Figure 2. Wind speed and direction forecast on Monday, July 29, 2013 at 11 am HST. Image credit: National Weather Service, Hawaii.
I will have an update by tomorrow for the latest on Flossie.
Updated: 8:54 PM GMT on July 28, 2013
Flossie weakening, but poses a threat to Hawaii
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.
Updated: 11:38 PM GMT on July 27, 2013