It’s that time of year when tropical storms and hurricanes are most prolific over the North Atlantic, Gulf of Mexico and northeastern Pacific, prime months for hurricanes being August to October when sea surface temperatures are at their warmest after heating up during the summer. However, there has been a record drought in Atlantic hurricanes directly hitting the U.S.A over the past seven years.
There have been only four direct strikes from hurricanes over the past seven years, the fewest in any seven-year stretch since reliable records began in 1851. This follows one of the most active periods for hurricanes impacting the U.S. between 2002-2008 – when 18 hurricanes hit the U.S. in a seven-year stretch. In fact, the last major hurricane to hit the U.S. – i.e. category three upwards, was Hurricane Wilma on 24/10/2005, nearly 11 years ago. Wilma battered Florida with 120mph winds and killed 35 people. However, the U.S. National Oceanic and Atmospheric Administration (NOAA) predicted back in May that a near-normal Atlantic hurricane season is likely this year - with 70% likelihood of 10-15 named storms. The Pacific has been unusually active recently, though.
One of the reasons for the dearth of hurricane activity over the north Atlantic has been attributed to the presence of an upper trough over the eastern U.S. – which has tended to steer any developing tropical storms and hurricanes away from the eastern side of the U.S. and out across the Atlantic.
Re-analysis of 500mb heights between August and October over recent years shows upper trough anomaly over eastern U.S. which has tended to steer hurricanes away from land.
Hurricane Hermine made landfall along the Florida Panhandle in the NW of the state early Friday morning (2nd September) local time as Category 1 Hurricane, with 80mph winds. It was the fourth hurricane of the 2016 Hurricane Season; Hermine developed from a long-tracked tropical wave that had previously crossed the Lesser and the Greater Antilles. It became the first hurricane to make landfall in Florida since Hurricane Wilma in 2005, and the first to develop in the Gulf of Mexico since Hurricane Ingrid in 2013. As well as the damage caused by the high winds, the hurricane dumped 1-2 feet of rain in places, causing flooding, highest total recorded was 22.36 inches in a location near Tampa on Florida’s west coast. There was also a storm surge along Gulf of Mexico coasts Florida, with mean high water levels some 6 feet above normal, causing some damage to coastlines.
(Image courtesy of The Weather Channel)
Hermine downgraded to a tropical storm as it passed over Georgia before moving NE out across the North Atlantic, now an ex-tropical cyclone. Although the storm is now over 300 miles off the eastern seaboard of the U.S., its winds have increased to near hurricane-strength today. Ex-TC Hermine is expected to move closer to NE U.S. by Wednesday, before turning away eastward and weakening towards Thursday. But for the next few days, there is a risk of coastal flooding, beach erosion, dangerously rough surf and winds gusts of 30 to 50mph, locally up to 60mph, along coasts from the mid-Atlantic states and along New England.
Although Hermine heads away from the U.S. out over the NW Atlantic later this week, it will not directly head towards the UK, as it is forecast to weaken considerably over the cold waters, before merging with low pressure moving out of NE Canada. Though residual warm moist air from Hermine meeting polar air further north may power up the jet coming out of eastern Canada, to perhaps deepen any depression coming east out over the NW Atlantic that could race towards the UK next weekend.
On the other side of North America, Tropical Storm Newton formed over the eastern Pacific on Sunday off the west coast of Mexico. The storm is currently 140 miles SW of Manzanillo and is forecast to track N/NW and strengthen, perhaps into a weak Cat. 1 Hurricane, as it makes landfall over southern Baja California peninsula in NW Mexico on Tuesday morning or afternoon local time. Newton then continuing north and making a second landfall on Wednesday after crossing the Gulf of California separating Baja California and mainland NW Mexico. Newton is forecast to produce heavy rainfall with totals of 5-10 inches for coastal areas, perhaps isolated totals of up to 15 inches. These large totals over normally arid areas of NW Mexico could cause life-threatening flash-floods and mudslides, particularly in the more mountainous areas.
After Newton makes its second landfall over NW Mexico, it will continue north into SW U.S. by Wednesday night as a tropical depression, bringing as much as 3-5 inches of rain to parts of Arizona and western New Mexico from Wednesday night through Thursday. This will bring some drought relief to the desert southwest of the U.S. – much of which is currently under a ‘moderate drought’. Though the heavy rain will bring the risk of flash-flooding.
Looking ahead at further tropical developments, there is a tropical wave over the eastern Caribbean and another wave over the eastern N Pacific, but only a 10% chance of either of these forming a tropical cyclone.