By Thursday, August 13, the tenth named storm of the 2020 Atlantic hurricane season is predicted to be prowling the open Atlantic. Tropical Depression 11 on Wednesday afternoon was on the verge of intensifying into Tropical Storm Josephine. Located more than 1,300 miles east of the northern Leeward Islands, TD 11 was heading just north of due west with top sustained winds of 35 mph, just below tropical storm strength.
TD 11 struggled to form a coherent structure early in the week. Bursts of showers and thunderstorms (convection) were displaced from the depression’s broad low-level circulation, a decoupling that made it more difficult for a symmetric low-level center to sharpen and intensify. A large swath of dry air also lurked to the north, but so far the system has retained a pocket of modestly moist air to support convection (mid-level relative humidity around 60%).
With upper-level wind shear expected to drop below 10 knots, and sea surface temperatures running around 28 degrees Celsius (82°F), computer models are in close agreement favoring a gradually strengthening Tropical Storm Josephine on Thursday and Friday. Well-established steering currents should take Josephine on a course just north of the Leeward Islands over the coming weekend, which would minimize any significant impacts.
By the August 15-16 weekend, the system will encounter increasing wind shear and dry air from a tropical upper-tropospheric trough. That encounter likely will lead to its weakening and perhaps to its dissipation. Even if it survives, Josephine most likely will recurve toward the north and northeast, staying well away from the U.S. East Coast.
A record year continues to set the pace
Assuming it forms as expected, Tropical Storm Josephine would be the earliest “J” storm on record for the Atlantic, well ahead of Tropical Storm Jose from August 25, 2005. Six more of the named storms in this hyperactive season have set similar marks, as shown at Wikipedia’s excellent compilation of Atlantic tropical cyclone records.
Arthur (May 17); record earliest January 3, 1938
Bertha (May 27); record earliest May 17, 1887
Cristobal (June 2); old record June 5, 2016
Dolly (June 23); record earliest June 20, 2016
Eduoard (July 6); old record July 11, 2005
Fay (July 9); old record July 21, 2005
Gonzalo (July 22); old record July 24, 2005
Hanna (July 24); old record August 3, 2005
Isaias (July 30); old record August 7, 2005
Another index of this year’s torrid pace: We are running more than two months ahead of the average formation date of the tenth named storm (October 19, based on the period 1966-2009).
Fortunately, the 2020 Atlantic season so far this year has spawned fewer and weaker hurricanes than its only rival, 2005. Among the latter year’s first nine named storms, four were hurricanes, including Cindy (peaking at Category 1 strength), Dennis (Cat 4), Emily (Cat 5), and Irene (Cat 2). Dennis led to 88 deaths and $2.5 billion in damage (USD 2005), mainly in the Florida Panhandle, while Irene caused 17 deaths and left a $1-billion trail of destruction from the Windward Islands to northeast Mexico and southern Texas.
By comparison, 2020 so far has brought just two hurricanes, Hanna and Isaias. Both were Category 1 storms.
What’s more concerning is that steering currents this year have been favoring U.S. landfalls. Five of the nine named storms so far have struck the United States, making this the earliest in any season that so many U.S. landfalls have occurred (the old record was August 18, 1916). The nation’s damage toll is also distressingly high for mid-August, including more than $4 billion from Isaias’s recent rampage up the East Coast with widespread high winds. Isaias caused more than 6 million power outages and spawned an estimated 37 tornadoes, including the longest-tracked tornado in Delaware history: 29 miles from Dover to Middletown.
Other U.S. damage estimates this year include $350 million from Hanna (Texas), $400 million from Tropical Storm Fay (East Coast), and at least $150 million from Tropical Storm Cristobal (Mississippi Valley).
The recurrence of weather setups favoring U.S. landfall is a worrisome sign heading into the climatologically busiest two months of hurricane season, from about mid-August to mid-October. Already, atmospheric and oceanic conditions are unnervingly aligned in favor of an extremely active few weeks to come. Unusually wet conditions in the Sahel region of Africa suggest that easterly waves that serve as seeds for tropical cyclones will continue to stream into the tropical Atlantic. Sea surface temperatures are warmer than average through nearly all of the western North Atlantic, providing ample fuel for hurricanes. And the tropical Pacific continues to shift toward La Niña conditions, which favor hurricane development in the Atlantic by reducing vertical wind shear there.
“Vertical wind shear in July has been extremely low, and there is typically strong persistence between July vertical wind shear and August-October-averaged vertical wind shear,” noted the forecast team from Colorado State University in its updated Atlantic seasonal outlook on August 5.
Both CSU and NOAA are now calling for the 2020 season to remain unusually active, perhaps continuing near the frenzied pace of 2005. That season produced not only the catastrophic hurricanes Katrina and Rita, but so many named storms in all (28) that the official list of 20 names was exhausted and the Greek alphabet was called into service for the only time on record.