Hurricane Season 2015: What it means for the Northeast
Hurricane season has been underway for a week now, and continues for six months (although the first storm of 2015, Tropical Storm Ana, formed in early May). Most forecasts are for a below average hurricane season. Those words sound comforting, but it is often said that “it only takes one” and that is certainly the truth.
2015 is expected to be an El Nino season, which historically has resulted in less activity. However, of the most damaging tropical cyclones in the Northeast since 1950, two of them – Agnes in 1972 and Bob in 1991 – took place in below normal hurricane seasons (7 storms and 8 storms, respectively). In addition, Bill in 2009 was a near-miss, passing east of New England as a Category 1 hurricane en route to Atlantic Canada. All those storms occurred during El Nino periods, with Agnes during what turned out to be a developing strong El Nino.
Upper-level air patterns
Looking at track patterns, the upper-level winds are most important in determining where storms are likely to go. There haven’t been recent trends determining potential storm tracks, and they are subject to change in relatively short notice as ridges and troughs develop. Tropical cyclones generally have the greatest impact on the Northeast after a landfall in the northern coast from New Jersey northward to central New England. However, significant impacts (particularly from rainfall, but also from wind) also can and do occur from storms making landfall farther south (particularly in the Carolinas but even in the Gulf of Mexico). In most cases, the storms need to be driven northward by a Bermuda High pattern located well to the east, allowing for a break to move the storm northward into a trough from 70-80°W longitude. A ridge farther east or a stronger, faster trough would likely turn the storm out to sea, while a ridge farther west or stronger would keep the storm moving westward into Florida, the Gulf of Mexico or the Caribbean.
It is nearly impossible to predict hurricane seasons, especially in the Northeast. There is no real correlation between Northeast impacts and ENSO status or season activity. 2005, the most active season on record and cataclysmic in the South (particularly with Hurricane Katrina), was quiet in the Northeast for the most part. 1954 and 1955, both of which were devastating years in the Northeast, were fairly quiet on the Gulf coast. As a result, everyone in the Northeast – from the Great Lakes to eastern Maine and south into the Mid-Atlantic – should be prepared for impacts this year. Even slower hurricane seasons have had severe impacts. Weaker storms can also be destructive – Diane in 1955 and Agnes in 1972 were only tropical storms and Irene in 2011 had also weakened when they made landfall closest to the Northeast, yet all three storms produced catastrophic flooding inland. Since most storms are transitioning to extratropical cyclones in the Northeast region, they tend to move fast and are often asymmetric as well with mostly wind to the east and mostly rain (often very heavy) to the west of the center. Past storms should not be used as guidance, since every storm is different – that was a deadly mistake made by many during Hurricane Sandy using their experience from the very different Hurricane Irene.
Just hope for the best and prepare for the worst! For instant weather tweets from me, follow @EternalWeather1 on Twitter.
Forecaster Craig Ceecee