The Atlantic was abuzz with tropical activity more typical of August than late June on Tuesday. The remnants of the season’s second landfalling storm, Danny, were pushing inland over the southeast U.S., and two tropical waves with the potential to develop into tropical storms, 95L and 97L, were speeding across the tropical Atlantic towards the Lesser Antilles Islands.

Danny: a minimum-impact landfall

Tropical Storm Danny formed off the coast of South Carolina at 3:05 p.m. EDT Monday, and made landfall in South Carolina at 8 p.m. EDT Monday evening as a minimal tropical storm with 40 mph winds. Danny lasted just eight hours as a tropical storm, falling to tropical depression strength Monday night as it pushed inland. Danny was declared post-tropical at 5 a.m. EDT Tuesday. Danny was a small tropical storm, and was moving fast enough that only a very small area of the coast received over an inch of rain. Soils were relatively dry in the regions affected by Danny’s rains, and there were no reports of damaging flooding.

Figure 1. Radar-estimated rainfall from Tropical Storm Danny, ending at 6:49 a.m. EDT June 29, 2021. Rainfall amounts in excess of two inches (yellow colors) affected a region less than 20 miles in diameter near the Georgia/South Carolina border. (Image credit: Weather Underground, an IBM company)

2021 is well ahead of climatology

Danny’s formation date of June 28 was nearly two months before the average August 23 arrival of the Atlantic’s fourth named storm, according to the National Hurricane Center. Only three Atlantic hurricane seasons have had four named storms develop earlier in the year: 2020, 2016, and 2012 (thanks go to Phil Klotzbach for this fact). The record-busy 2020 season had its fourth named storm on June 23 and fifth named storm on July 6; this was the earliest fifth storm on record in the Atlantic.

Danny is already the second U.S. landfalling storm of 2021, following Claudette. This is behind the record pace of the 2020 hurricane season, when the second U.S. landfall (Cristobal in southeast Louisiana) occurred on June 7. Last year had a record 11 named storms make landfall in the contiguous U.S., beating the old record of nine set in 1916. The third U.S. landfall of 2020 (Fay in New Jersey) occurred on July 10.

Figure 2. The National Hurricane Center’s Tropical Weather Outlook from 8 a.m. EDT Tuesday, June 29. Tropical disturbances 95L (orange colors) and 97L (yellow colors) were both highlighted.

Disturbance 95L in central tropical Atlantic remains disorganized

In the central tropical Atlantic, a tropical wave designated 95L was headed west to west-northwest at about 15-20 mph on Tuesday afternoon. 95L had marginal conditions for development, with sea surface temperatures near 26.5 degrees Celsius (80°F); 95L’s position close to the equator (about 12°N latitude) was also limiting its ability to use Earth’s spin to help get itself spinning.

Satellite images showed 95L to be medium-sized, with a moderate amount of spin, but no signs of a surface circulation. The system was more organized than on Monday, with a prominent curved band of heavy thunderstorms along the north side of its center. The atmosphere surrounding 95L was not especially moist, with a mid-level relative humidity of 60-65%, thanks to the presence of the dry air of the Saharan Air Layer to the north and west. Wind shear was light to moderate, at 5-15 knots; this amount of wind shear was strong enough to drive dry air into the system’s core, disrupting it.

Forecast for 95L

As 95L progresses west to west-northwest at about 15-20 mph through Wednesday morning, it will continue to struggle with marginal sea surface temperatures and dry air from the Saharan Air Layer, though wind shear of 5-15 knots will be favorable for development, according to the 12Z Tuesday run of the SHIPS model. On Wednesday evening, when 95L will be nearing the Lesser Antilles Islands, sea surface temperatures will warm to 27.5 degrees Celsius (82°F), making it more likely 95L could wall off the dry air and form a strong inner core region of heavy thunderstorms resistant to the dry air. The system’s more northerly position, farther from the equator, will aid this process.

Steering currents will likely carry 95L through the Lesser Antilles Islands on Wednesday night, bringing gusty winds and heavy rains. Many of these islands, with a much drier-than-average May, could benefit from the rain. 95L will continue west-northwest on Thursday, and will likely affect Puerto Rico and the eastern Dominican Republic on Thursday night. Land interaction with the high terrain of Hispaniola may significantly disrupt 95L, though residents of the Turks and Caicos Islands and the southeast Bahamas could still see heavy rains from 95L beginning on Friday.

Two of the three best models for predicting tropical cyclone genesis – the European and GFS models – support some limited development of 95L, and a number of their ensemble members develop 95L into a tropical storm by late this week. In an 8 a.m. EDT Tuesday Tropical Weather Outlook, the National Hurricane Center gave 95L two-day and five-day odds of formation of 30% and 40%, respectively. The next name on the Atlantic list of storms is Elsa, a name that is debuting this year after Tropical Storm Erika in 2015 caused enough damage in Dominica to make it one of just two tropical storms on record to have its name retired (the other was Tropical Storm Allison in 2001). Any nation impacted by a severe hurricane or tropical storm can lobby the World Meteorological Organization to have the name of that storm retired.

Disturbance 97L in central tropical Atlantic

About two days’ travel behind 95L is another tropical wave, midway between Africa and the Lesser Antilles, designated 97L on Tuesday morning by the National Hurricane Center. 97L was headed west at about 20 mph on Tuesday afternoon, and was positioned at a very low latitude, near 8°, as seen on satellite images. This position close to the equator will keep any development of 97L slow to occur, as will the relatively large size of the system, and the fact that it is embedded in the Intertropical Convergence Zone (ITCZ), the semi-permanent band of heavy thunderstorms that circles the globe in the tropics. Developing tropical cyclones in the ITCZ often have trouble consolidating around a single surface circulation center, as there tend to be multiple regions of spin that compete with each other. However, 97L had favorable conditions for development otherwise, with sea surface temperatures near 28 degrees Celsius (82°F), moderate wind shear of 10-20 knots, and a very moist atmosphere with a mid-level relative humidity of 80%.

Forecast for 97L

As 97L progresses west to west-northwest at about 15-20 mph this week, it will stay well south of the dry air from the Saharan Air Layer, and potentially benefit from a moister atmosphere left behind by the passage of 95L in front of it. Conditions will be favorable for development, according to the 12Z Tuesday run of the SHIPS model, with moderate wind shear of 10-20 knots and sea surface temperatures near 28 degrees Celsius (82°F). Also favoring intensification will be a large-scale region of ascending air over the Atlantic, caused by passage Thursday and Friday of an atmospheric disturbance called a Convectively Coupled Kelvin Wave, as explained in a Tweet by Eric Webb.

Steering currents will likely carry 97L into the Lesser Antilles Islands by Friday night, bringing gusty winds and heavy rains. Once 97L enters the eastern Caribbean on Saturday, it will encounter an area where the surface trade winds speed up. This speed-up creates a bit of a vacuum at the surface that forces air from aloft to sink, creating a more stable atmosphere hostile to tropical storms. This situation makes the eastern Caribbean something of a hurricane graveyard, as referred to in the Tweet below by NOAA hurricane scientist Andy Hazelton, which showcases model tracks from the 0Z Tuesday run of the European model ensemble.

Two of the three best models for predicting tropical cyclone genesis – the European and GFS models – support some limited development of 97L, and a number of their ensemble members develop 97L into a tropical storm by late this week. The operational run of the 6Z Tuesday GFS model was eye-opening, predicting that 97L would develop into a long-track Cape Verdes-type hurricane crossing the length of the Caribbean. The 12Z Tuesday run of the model backed off from this prediction, though. In an 8 a.m. EDT Tuesday Tropical Weather Outlook, NHC gave 97L two-day and five-day formation odds of 10% and 20%, respectively.

Hurricane Enrique kills 2 in Mexico

The first hurricane of the season in the Eastern Pacific, Enrique, brought torrential rains and damaging flooding and mudslides to the coast of southwestern Mexico on Monday, after passing just offshore as a category 1 hurricane with 85 mph winds. According to floodlist.com, Enrique killed two people in Mexico, damaged hundreds of homes, and washed out roads and bridges. As seen in the Tweet below, Enrique brought severe flooding on Monday to Lázaro Cárdenas, in southwestern Mexico’s Michoacán state.

At 11 a.m. EDT Tuesday, Enrique was a much-weakened tropical storm with 40 mph winds, moving north-northwest at 8 mph towards Mexico’s Baja Peninsula. Enrique is expected to make landfall there on Wednesday morning, bringing 2-4 inches of rain, with isolated maximum amounts of 6 inches. Enrique is also expected to bring 3-6 inches of rain across Sinola, western Durango and southern Chihuahua in western Mexico. Dry air flowing from the interior of Mexico will continue to weaken Enrique, and the storm will likely be downgraded to a tropical depression by Wednesday.

A surge of moisture associated with Enrique is likely to push northwestward Wednesday through Friday, bringing a bit of drought relief to northwestern Mexico, Arizona, and New Mexico.

Bob Henson contributed to this post.

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Jeff Masters

Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...