Satellite image
Tropical Storm Edouard southeast of Newfoundland, Canada, at 8 a.m. EDT July 6, 2020. (Image credit: NOAA/RAMMB)

Mother Nature put on her own modest Fourth of July fireworks over the weekend, when Tropical Depression 5 formed near Bermuda on July 4. Despite marginal conditions for development – sea surface temperatures (SSTs) near 25 degrees Celsius (77°F), moderate wind shear, and dry air – TD 5 managed to intensify into Tropical Storm Edouard at 11 p.m. EDT July 5. By 11 a.m. EDT July 6, Edouard had intensified to 45 mph winds as it sped northeast at 37 mph over the open Atlantic.

Edouard was the earliest fifth Atlantic named storm formation on record, beating the record set by Emily on July 12, 2005. The fifth named storm of the year typically does not occur until August 31, so we are nearly two months ahead of climatology. None of this year’s named storms have been hurricanes, and the first hurricane of the season usually arrives by August 10.

According to the Colorado State University real-time hurricane activity site, the North Atlantic has had about 340% of the usual amount of Accumulated Cyclone Energy, or ACE, by July 6: 6.5 units, compared to the 30-year average of 1.9 units. For comparison, the Northeast Pacific has had 3% of its average ACE expected by that same date; the Northwest Pacific 17%; and the North Indian Ocean 234%. All told, the Northern Hemisphere is running at less than half of its usual activity up as of July 6, as the Pacific normally produces the great majority of the hemisphere’s ACE up to that date.

Edouard passed very close to Bermuda as a tropical depression on the morning of July 5, bringing moderate rains and gusty winds. The Bermuda airport recorded peak sustained winds of 25 mph at 7:09 a.m. Atlantic Standard Time July 5. No other land areas will be affected by Edouard, which is expected to be destroyed by cold waters, strong wind shear, and a frontal zone that will absorb it on Tuesday. Edouard is the type of weak and short-lived storm that might have not been named before the satellite era.

Bermuda radar image
Figure 1. Bermuda radar as seen at 9:55 a.m. AST July 5, 2020, when a band of rain from Tropical Depression 5 was affecting the island. The depression became Tropical Storm Edouard later that night. (Image credit: Bermuda Weather Service)

A harbinger of an active Atlantic hurricane season?

It is disconcerting to see 2020 beat the record for the busiest start to the Atlantic hurricane season, surpassing 2005. That unforgettable year went on to set all-time records with 28 named storms, 15 hurricanes, seven major hurricanes, and four category 5 hurricanes (Emily, Katrina, Rita, and Wilma). However, the early season activity of 2020 differs in character from that of 2005 and does not necessarily portend an active peak portion of hurricane season.

Four of the first five storms of 2005 formed in the deep tropics, and three became hurricanes – two of them major hurricanes. In contrast, only one of 2020’s first five storms formed in the deep tropics (Cristobal, in the Gulf of Mexico’s Bay of Campeche), and none became hurricanes. As Phil Klotzbach and Bill Gray, since deceased, of Colorado State’s seasonal hurricane forecasting team wrote in 2013:

Most years do not have named storm formations in June and July in the tropical Atlantic (south of 23.5°N); however, if tropical formations do occur, it indicates that a very active hurricane season is likely. For example, the seven years with the most named storm days in the deep tropics in June and July (since 1949) are 1966, 1969, 1995, 1996, 1998, 2005, and 2008. All seven of these seasons were very active. When storms form in the deep tropics in the early part of the hurricane season, it indicates that conditions are already very favorable for tropical cyclone development. In general, the start of the hurricane season is restricted by thermodynamics (warm SSTs, unstable lapse rates), and therefore deep tropical activity early in the hurricane season implies that the thermodynamics are already quite favorable for tropical cyclone development.

Ocean Heat Content
Figure 2. Total oceanic heat content (also called the Tropical Cyclone Heat Potential, or TCHP) in kilojoules per square centimeter (kJ/cm^2), for July 5 in 2005 and 2020. TCHP was at record values over much of the Caribbean, Gulf of Mexico, and waters surrounding the Bahamas in July 2020. TCHP in excess of 90 kJ/cm^2 (orange colors) is commonly associated with rapid intensification of hurricanes. (Image credit: University of Miami Rosenstiel School)

While it is heartening that none of the early-season named storms of 2020 formed in the deep tropics, it is unsettling to compare the amount of ocean heat energy available to power Atlantic hurricanes in 2020 with that available in 2005. The comparison (Figure 2) shows that more heat energy is available in 2020 than was the case in 2005 in many regions, so there is a high likelihood of seeing very intense hurricanes in 2020. But there’s some good news too: 2020 is missing a big ocean heat hotspot in the central Gulf of Mexico such as occurred in 2005, when a large warm eddy that broke from the Loop Current helped fuel the rapid intensification of hurricanes Katrina and Rita.

Precipitation forecast
Figure 3. Precipitation forecast for the five-day period ending at 8 a.m. EDT Saturday, July 11, 2020. (Image credit: NOAA)

Next storm possible late this week off North Carolina

A small area of low pressure that formed on July 5 along an old cold front along the Florida Panhandle coast moved inland to the northeast on the morning of July 6. This low, designated 98L by NOAA’s National Hurricane Center, is expected to grow in size and possibly emerge off the coast of North Carolina by mid-week. The system is expected to move north to northeast and hug the mid-Atlantic coast late in the week. Proximity to land will likely hinder development, but if the low’s center of circulation emerges and moves over the core of the Gulf Stream current just off the coast, it may intensify into a tropical storm. Regardless of development, 98L likely will bring heavy rains of 3 to 6 inches to portions of coastal South Carolina and North Carolina (Figure 3). In its 2 p.m. EDT July 6 Tropical Weather Outlook, NHC gave 98L two-day and five-day odds of development of 10% and 40%, respectively.

The next name on the Atlantic list of storms is Fay. The earliest formation of the season’s “F” storm came on July 22, 2005, with Tropical Storm Franklin.

Satellite imageHow climate change is making hurricanes more dangerous

The deep tropics are dominated by dry, stable air, because of repeated incursions of air from the Saharan Air Layer from Africa. This is a common situation in July, which explains why so little hurricane activity typically occurs during the month. The best models for predicting tropical cyclone genesis – the European, GFS, and UKMET models – continue to show little or no support for anything developing in the tropical Atlantic through mid-July.

Bob Henson contributed to this post.

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Topics: Climate Science, Weather Extremes