Hurricanes Florence and Olivia Executive Summary FLORENCE Is About to Become a Major Hurricane

eVENT Willis Research Network Hurricane Commentary

Hurricanes Florence and Olivia Executive Summary FLORENCE is about to become a major hurricane. The most likely scenario is a major hurricane landfall in the Southeast U.S., but no landfall is still a possibility. A scenario of a stalled hurricane on the U.S. East Coast is possible with torrential rains and flooding. OLIVIA continues on a track towards Hawaii with possible landfall as a Tropical Storm late Tuesday. It’s still too early to pinpoint which Island, if any, will receive a direct landfall.

FLORENCE 5am EDT Sept 10, 2018 Date/Time Location 24.9N, 58.9W Windspeed/Pressure 105mph, 969mb Speed/Direction 9mph WNW

OLIVIA 8am EDT Sept 10, 2018 Date/Time Location 21.7N, 147.6W Windspeed/Pressure 85mph, 980mb Speed/Direction 10mph W

Forecast Summary The peak of the hurricane season is certainly living up to its name this year. Three hurricanes roam the Atlantic, a potential disturbance is about to enter the Gulf of Mexico, and a string of storms line the tropical Pacific. This commentary focuses on the two most dangerous storms for the U.S.: FLORENCE and OLIVIA

FLORENCE

FLORENCE is rapidly intensifying. At the time of writing, wind speeds are on the threshold of Major Hurricane status. Ocean temperatures are warm - and the warmth extends to a great depth – providing more than enough fuel to feed a major hurricane. Winds aloft are generally light which will allow the storm to mature and establish a robust structure. Category 4 status is likely by Tuesday (Figure 1) and major hurricane status is likely until a probable Southeast U.S. landfall.

In yesterday’s commentary we identified a patch of thunderstorms in FLORENCE’s path. This area of disturbed weather has weakened somewhat and should not interfere too strongly with the forecast path or intensity. FLORENCE will ingest these thunderstorms and, if anything, grow larger.

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FLORENCE’s forecast tracks from the different forecasting centers are in remarkable agreement (Figure 1). This is because the guiding environmental winds around the southern side of the subtropical high are fairly predictable. North Carolina appears to be a focus but landfall is possible anywhere from Georgia to New Jersey. There’s also a smaller possibility of no landfall at all.

However, FLORENCE’s forward speed may slow down close to possible landfall as it comes up against a developing high-pressure region over the Ohio Valley. A dangerous scenario is coming into focus for a stalled hurricane on the U.S. East Coast. Rainfall amounts greater than 20 inches are possible under this scenario, with 10+ inches widespread across broad swaths of the U.S. East Coast. But it’s still too early to confidently assess the likelihood of this scenario.

Figure 1: The latest model forecast tracks and intensity for Hurricane Florence. Source: NCAR/TCGP. For updated forecasts, please visit: http://www.ral.ucar.edu/hurricanes/realtime/current/

OLIVIA

OLIVIA continues on a trajectory towards the Hawaiian Islands. A hurricane approaching Hawaii from the east-northeast (Figure 2) has no precedent in the historical record. Usually the ocean temperatures are too cool and the air too dry. However, the current environment is supportive. Even so, OLIVIA will start to encounter less favorable conditions in 36-48 hours and is forecast to weaken to a Tropical Storm before possible landfall (Figure 2).

The forecast cone contains the major Islands of the Hawaiian chain. It’s still too early to pinpoint which Island will experience a direct landfall. There’s also the possibility that OLIVIA may track between gaps in the Islands. If that happens, the storm is still large even to bring heavy rains and tropical storm force winds to the Islands. Rainfall totals will not approach those seen in Hurricane Lane but flooding is likely.

Figure 2: The latest model forecast tracks and intensity for Hurricane Olivia. Source: NCAR/TCGP. For updated forecasts, please visit: http://www.ral.ucar.edu/hurricanes/realtime/current/

For further information please contact

Geoffrey Saville Dr. James Done Roy Cloutier Willis Research Fellow Senior Research Manager Catastrophe Analytics Capacity Center for Climate and Weather Extremes Willis Research Network Atmospheric Hub Willis Re Inc. Willis Towers Watson National Center for Atmospheric Research 8400 Normandale Lake Blvd Willis Group Limited Bloomington, MN 55437 P.O. Box 3000, Boulder, CO 80307 20th Level The Willis Building 51 Lime Tel: +1 (952) 841-6652 Tel: +1 (303) 497-8209 Street EC3M 7DQ. Email: [email protected] Email: [email protected] Tel: +44 203 124 8858 Website: Website: https://www.c3we.ucar.edu/ Email: http://www.willisresearchnetwork.com/ http://staff.ucar.edu/users/done [email protected]

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