Hurricane Michael Executive Summary MICHAEL Is Forecast to Make Landfall Along the Northeastern Gulf Coast As a Major Hurricane

eVENT Willis Research Network Hurricane Commentary

Hurricane Michael Executive Summary MICHAEL is forecast to make landfall along the northeastern Gulf Coast as a Major Hurricane. Likely impacts are Category 3 strength winds and destructive storm surge. Tropical storm strength winds and flash flooding may extend far inland across Georgia and the Carolinas.

MICHAEL 1pm CDT Oct 9, 2018 Date/Time Location 25.4N, 86.4W Windspeed/Pressure 110mph, 965mb Speed/Direction 12mph N

Forecast Summary Overnight Monday, MICHAEL struggled against upper-level winds. The satellite image above shows most of the thunderstorm activity (red colors) pushed off to the northwest side. However, MICHAEL’s structure is now organizing into a more typical circular storm. Boosted by the warm waters of the Gulf of Mexico, MICHAEL is poised to reach major hurricane status, sustaining category 3 wind speeds. The warm waters of the Gulf of Mexico extend to great depth. This will limit any upwelling of cooler water, that can act to weaken the hurricane.

MICHAEL is accelerating along a northward track towards the Gulf Coast. Forecast guidance is in higher-than-normal agreement for a landfall along the northeastern Gulf Coast (Figure 1). The region between Pensacola and Apalachicola is at highest risk of a direct landfall. But storm surge and damaging winds will extend over a broader region. After landfall, MICHAEL is forecast to zip across the southeastern U.S. States bringing tropical storm strength winds with flash flooding possible. But major river flooding, as we saw from Hurricane Florence, is not expected. MICHAEL may even re-strengthen as it emerges off the U.S. East Coast.

The most likely landfall intensity is category 3 (Figure 1). But a category 2 or category 4 landfall are possible. The actual landfall category will depend on how quickly the storm can organize a circular and robust hurricane structure. A more organized storm has a higher likelihood of attaining category 4 wind speeds.

MICHAEL is a medium-sized hurricane, in terms of its area of damaging winds. It is smaller than Hurricane Ivan (2004) but larger than Hurricane Dennis (2005). We know that size can play a major role in the resulting damage. Large Hurricane Ivan, for example, generated seven times the insured losses than from smaller Hurricane Dennis, despite making landfall in a similar location near the border of Florida and Alabama.

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Storm surge is one of the major expected impacts. Waters are already 1-2 feet above normal due to sustained onshore winds. The northeastern Gulf Coast has a history of landfalling hurricanes bringing destructive surge. We therefore know from experience that the region’s shallow coastal waters make it particularly vulnerable. MICHAEL may bring up to 12 feet of surge in some locations.

Figure 1: The latest model forecast tracks and intensity for Hurricane Michael. 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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