HURRICANE COMMENTARY

Hurricane IRENE Date/Time: 1000CDT 08/24/11

Location: 22.4N, 73.9W 285 miles SE of Nassau, Bahamas

Windspeed/Pressure: 115mph, 956mb (Category 3 Hurricane)

Speed/Direction: 12mph NW

Executive Summary

Hurricane IRENE has become a major hurricane and has begun to impact the

Bahamas. Further strengthening is expected in the next 48 hours. The likely future track for IRENE takes it to the east of before bearing down on . We estimate a greater than 50% chance that IRENE makes a between and . Satellite Image of HU IRENE (image from NOAA/GOES)

This morning Hurricane IRENE became a major hurricane as it prepared to enter . IRENE is a Category 3 hurricane with 115mph sustained winds. IRENE has good presentation on satellite with a clear and good outflow; the NHC is expecting IRENE to strengthen further over the next 24-48 hours. IRENE has a relatively compact core of hurricane force winds (they extend 50 miles from the center) but a much larger expanse of tropical storm force winds (up to 205 miles from the center). IRENE has a CME Hurricane Index (CHI) value of 6.8. IRENE is expected to bring hurricane and/or tropical storm force winds to much of the Bahamas over the next 24-48 hours and, as such, the Government of the Bahamas has placed most of the islands under a hurricane warning.

Since our last commentary 48 hours ago, the model forecasts for IRENE have come into solid alignment after shifting to the east. We can now discount a landfall along the coast and along the and South Carolina coasts. The model consensus (figure 1) predicts that IRENE will begin to recurve to the northeast in the next 48 hours, after passing through the Bahamas. A landfall along the extreme eastern part of (i.e. Cape Hatteras) is possible but increasingly unlikely; a close approach on Saturday is the most likely outcome. After this time the models begin to diverge; they all agree that IRENE will continue northeastwards and will increase in speed but the precise direction is uncertain. This places most of the US coast from to and into Maine as potential landfall sites by the end of the weekend. The model consensus has a landfall near the eastern tip of Long Island or in the /Cape Cod area on Sunday night. There is also a healthy chance that IRENE could miss the US coast altogether and eventually impact the Canadian Maritimes.

As regards intensity, there is little reason to believe that IRENE will not continue to intensify. It will shortly be over the very warm Gulf Stream which it will traverse until it reaches at least Cape Hatteras. Wind shear remains low (IRENE’s track takes it around a pocket of higher wind shear) and moist air is plentiful. In short, we would not be surprised if IRENE becomes at least a Category 4 hurricane in the next 48 hours. After passing Cape Hatteras, the environment for IRENE will begin to degrade but, provided IRENE can move relatively swiftly, it could well retain Category 1 or 2 status when it reaches the New England coast.

Given the track and intensity potentials, we would handicap the future of IRENE as follows:  A close approach (or hit) to Cape Hatteras on Saturday before reaching eastern New England on Sunday – 40%  A close approach to Cape Hatteras on Saturday before reaching Long Island on Sunday – 20%  A close approach to Cape Hatteras on Saturday and then missing the US coast – 40%

Historically, we have identified two storms from the 1954 season which might provide instructive analogs – CAROL and EDNA (figure 2). Both passed just to the east of Cape Hatteras before heading towards New England. CAROL reached eastern Long Island as a borderline Cat 1-2 hurricane and caused in excess of $400M in damage (1954 Dollars) ; EDNA hit Cape Cod as a Cat 1 hurricane causing $40M of damage (1954 Dollars). That CAROL caused more damage than EDNA is a function both of CAROL’s greater strength and landfall location (landing on Long Island allowed CAROL to cause damage to Long Island itself, , Rhode Island and ). Given the increase in property and property values in the region we would expect multi-billion dollar losses from these storms today.

© Copyright 2011 Willis Limited/Willis Re Inc. All rights reserved: No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, whether electronic, mechanical, photocopying, recording, or otherwise, without the permission of Willis Limited/Willis Re Inc. Some information contained in this report may be compiled from third party sources; however, we do not guarantee and are not responsible for the accuracy of such. This report is for general guidance only, is not intended to be relied upon, and any action based on or in connection with anything contained herein should be taken only after obtaining specific advice. The views expressed in this report are not necessarily those of Willis Limited/Willis Re Inc., or any of its/their parent or sister companies, subsidiaries or affiliates (hereinafter “Willis“). Willis accepts no responsibility for the content or quality of any third party websites to which we refer. 1 of 1

HURRICANE COMMENTARY

Figure 1: Model forecasts for Hurricane IRENE as at 0600UT 08/24/11

Figure 2: Hurricane IRENE (official forecast track; solid line), 1954 (Long Island landfalling track) and 1954 (Cape Cod landfalling track)

For more information on this commentary, please contact:

Dr. Steve Smith [email protected] +1 312 288 7483 2 of 2