The peak portion of the Atlantic hurricane season is at hand, and the tropics are buzzing with activity typical for the last week of August. For the next six weeks, we can expect a host of tropical disturbances capable of developing into tropical depressions to roll off the coast of Africa or form in the subtropics (like Henri did). The next two names on the Atlantic list of storms are Ida and Julian; we expect to see both of these names used before the end of August.

Figure 1. Five-day Tropical Weather Outlook issued by the National Hurricane Center at 2 p.m. EDT Tuesday, August 24, 2021. (Image credit: NHC)

Caribbean disturbance a threat to Central America, Mexico, and Texas

The National Hurricane Center (NHC) Tuesday was tracking three disturbances capable of developing into tropical depressions. Only one of these appeared to be an eventual threat to land – a tropical wave in the eastern Caribbean that may develop late this week as it moves west. This system was headed west at 10-15 mph, and was highly disorganized given prohibitively high wind shear of 30-40 knots.

Figure 2. Infrared satellite image of a broad area of disturbed weather in the southeast Caribbean at 1710Z (1:10 p.m. EDT) Tuesday, August 24, 2021. (Image credit: RAMMB/CIRA/CSU).

By Friday, the wave is expected to reach the western Caribbean near the coast of Honduras, where wind shear is expected to decrease enough for the system to grow more organized. Heavy rains from the disturbance are likely to affect the coasts of Nicaragua and Honduras beginning on Friday morning, and these heavy rains will spread to Belize and Mexico’s Yucatan Peninsula on Saturday. One of the top three models for predicting tropical cyclone genesis, the GFS, predicted with its Tuesday morning run that the disturbance would make landfall on Saturday in the Yucatan Peninsula as a weak tropical storm.

There is stronger model support for the wave to develop once it enters the southwestern Gulf of Mexico on Sunday. Steering currents favor a west-northwest to northwest motion for the system, and Texas and Mexico appear at risk for a landfalling named storm on Monday or Tuesday. In its 2 p.m. EDT Tuesday Tropical Weather Outlook, the NHC gave the system 2-day and 5-day odds of development of 10% and 60%, respectively.

Figure 3. Visible satellite image of disturbance 97L in the central tropical Atlantic at 1745Z (1:45 p.m. EDT) Tuesday, August 24, 2021. (Image credit: tropicaltidbits.com)

97L may develop late this week

Disturbance 97L is slowly consolidating in the central Atlantic nearly 1,000 miles east-northeast of the Leeward Islands. A low-level swirl was clearly evident at midday Tuesday, moving northwest from this area. However, most of the showers and thunderstorm activity (convection) associated with 97L remained well to the southeast of this swirl. Moreover, a large field of dry air associated with the Saharan Air Layer was lurking just east of 97L, and dry air will continue to infiltrate this system over the next several days.

Otherwise, conditions likely will become increasingly favorable for 97L to develop. Sea surface temperatures below its path will rise from around 27 degrees Celsius (81°F) on Tuesday to 28-29°C (82-84°F) by Wednesday, and wind shear will decrease from a strong 15-20 knots on Tuesday to 10 knots or less by Thursday. NHC gives 97L a 20 percent chance of developing into at least a tropical depression by Thursday and a 70 percent chance by Sunday.

If it does survive its currently tough environment and goes on to develop, some models support 97L’s intensifying this weekend in the central Atlantic, perhaps becoming a named storm. Beyond that point, strong model agreement suggests that steering currents will haul 97L to the northeast, away from the western Atlantic.

Figure 4. Infrared satellite image of disturbance 98L in the eastern tropical Atlantic at 1815Z (2:15 p.m. EDT) Tuesday, August 24, 2021. (Image credit: tropicaltidbits.com)

Another one to watch: 98L

A few hundred miles south-southwest of the Cabo Verde Islands, 98L may get its act together more quickly than 97L. A large field of convection was moving west at 10-15 knots, maintaining its strength even during the normally quiet part of the convective day in the tropics. 98L for the next several days will be passing over warm waters with sea surface temperatures (SSTs) of 27-28 degrees Celsius (81-82°F). The atmosphere surrounding 98L is moist, with a mid-level relative humidity around 65%, and wind shear will decrease from the current 15-20 knots to 10 knots or less by Wednesday and Thursday.

NHC gives 98L a 3- and 5-day chance of development of 20 and 30 percent; it would not be a surprise to see 98L beating those three-day odds. There is only limited model support for 98L by later in the week, as it encounters greater wind shear and a drier atmosphere on its west-northwest trek.

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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...

Bob Henson

Bob Henson is a meteorologist and journalist based in Boulder, Colorado. He has written on weather and climate for the National Center for Atmospheric Research, Weather Underground, and many freelance...