Although the Atlantic currently has no tropical cyclones active, there are four systems being monitored for potential development. The first, Invest 97L, is an area of low pressure east of the Windward Islands which is headed for less favorable conditions, and development appears unlikely. The second, Invest 98L, is a broad area of low pressure southeast of Bermuda, which could gradually gain tropical characteristics some time next week. The third, Invest 99L, is a vigorous tropical wave which has recently emerged off Africa. The fourth is a non-tropical area of low pressure which is expected to develop southwest of the Azores this weekend, and likely has the highest chance of becoming a named storm. None of these systems pose an imminent threat to land, though Invest 99L has a chance to affect the Lesser Antilles in a week or so.

Invest 97L likely out of time to develop as it enters a hostile environment

As of 18:00 UTC Friday, Invest 97L was located near 12.8°N 52.5°W, and was moving generally west-northwestward. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1010 mb. 97L consists of an exposed low-level swirl with some poorly organized convection to the east, indicative of strong westerly shear tearing apart the system. Although 97L is located over warm waters above 28°C (82.4°F), the vertical shear is currently analyzed to be over 25 knots (30 mph) over 97L, and the shear is expected to remain strong over the next several days. In addition, a dry mid-level atmosphere with relative humidity values below 50 percent should limit development of 97L. None of the global models predict that 97L will develop into a tropical cyclone. The National Hurricane Center (NHC) currently gives 97L only a 10 percent chance of development, both within 48 hours and five days.

Invest 98L could develop off the Southeast United States coast next week, but dry air likely to limit significant development

As of 18:00 UTC Friday, Invest 98L was located near 30.8°N 63.7°W, and was moving southwestward. Maximum sustained winds were 30 knots (35 mph), with an estimated minimum pressure of 1010 mb. The extratropical remnants of Hurricane Florence have split up into two separate entities, with 98L moving off to the southwest and detaching from the front. 98L currently consists of an exposed, elongated low-level circulation, with minimal convective activity. Although 98L was not far off from becoming a tropical storm yesterday as it had a well-defined circulation with deep convection near the center, 98L became significantly less organized overnight due to dry air and strong upper-level winds. 98L is expected to remain over waters near 29°C (84.2°F) for the next several days, which is favorable for development. In addition, wind shear is expected to drop to the favorable range (less than 10 knots) from about 36-72 hours. Potentially suppressing development is the presence of mid-level dry air, with mid-level relative humidity values expected to remain below 40 percent for the next few days. Likely as a result of the dry air, global models do not show significant development with this system, which is good news for the Carolinas, as they are still dealing with effects of Hurricane Florence. Regardless, interests along the Southeastern United States coast should monitor 98L, even though I think it’s unlikely that it will significantly affect any land areas. The NHC gives 98L a near zero percent chance of development within 48 hours, but a 30 percent chance within five days.

Invest 99L, a vigorous tropical wave, may develop east of the Lesser Antilles next week

An impressive low-latitude tropical wave which exited the coast of western Africa Friday morning has been designated Invest 99L. As of 18:00 UTC Friday, Invest 99L was located near 6.8°N 19.3°W, and was moving generally westward. Maximum sustained winds were 30 knots (35 mph), with an estimated minimum pressure of 1008 mb. 99L is already well-organized, though convective activity has waned this afternoon. Although 99L is expected to remain in a low-shear (less than 10 knots), warm water (sea surface temperatures above 27°C/80.6°F) environment for the next several days, 99L’s quick movement and low latitude will likely limit significant development in the short term. This is reflected in the global models. The 12z ECMWF and GFS models both develop 99L slightly east of the Windward Islands by the middle of next week, but neither depicted significant development at this time. The 12z UKMET model run did not develop 99L. The NHC currently gives 99L a 30 percent chance of development within 48 hours and a 60 percent chance within five days. Based on the lack of model support, I personally place these odds slightly lower, at 20 percent within 48 hours and 40 percent within five days.

Non-tropical area of low pressure system likely to develop into a subtropical or tropical cyclone over central Atlantic by Monday

The fourth system, and perhaps most likely to develop of all four, is a non-tropical low that is expected to develop over the central Atlantic by tomorrow. It is likely to develop a well-defined circulation on Sunday, and will likely acquire subtropical or tropical characteristics after that time. This large system is likely to meander over the open Atlantic for several days, but may not ever have the characteristics of a fully tropical cyclone. It has not yet been designated an “invest” but likely will be soon. The 12z GFS, ECMWF, and UKMET models all develop this system, and I personally think it is the most likely to be Kirk. It does not look likely that this system will pose any threat to any land areas in the short term. The NHC gives this system a 20 percent chance of development within 48 hours, and a 70 percent chance within five days.

The next name on the Atlantic naming list is Kirk.