It looks much more like September than late June over the deep tropical Atlantic, with two tropical waves currently being monitored by the National Hurricane Center for development. Invest 95L, located east of the Lesser Antilles, has not become much better organized, and its development chances appear to be decreasing. However, newly-designated Invest 97L over the southeastern tropical Atlantic is looking increasingly likely to be the Atlantic’s first deep tropics cyclone of 2021. Should either or both of 95L or 97L develop, it would likely suggest an active 2021 Atlantic hurricane season is in the cards, as named storm development in the deep tropical Atlantic prior to August is typically correlated with above-average Atlantic hurricane seasons. The next two names on the Atlantic naming list are Elsa and Fred.

As of 18:00 UTC Tuesday, Invest 95L was centered near 12.4°N 50.3°W. Maximum sustained winds were 30 knots (35 mph), with an estimated minimum pressure of 1011 mb. 95L is producing disorganized showers and thunderstorms, and continues to lack a well-defined circulation. The National Hurricane Center (NHC) gives 95L a 20 percent chance of development within 48 hours and a 30 percent chance within five days, slightly lower chances than yesterday. 95L lacks significant model support for development, with the latest runs of the GFS, ECMWF and UKMET models all not developing it into a tropical cyclone. Although 95L is moving into warmer sea surface temperatures greater than 27°C (80.6°F), in about 24 hours, 95L’s forward speed is expected to increase to greater than 20 knots (25 mph), which will make it difficult to close off a well-defined circulation necessary for tropical cyclone designation. In addition, a relatively dry mid-level environment with 500-700 mb relative humidity values of 60 percent will likely limit development. I think 97L, the tropical wave to the southeast of 95L has a much better shot at development (more on 97L below).

As of 18:00 UTC Tuesday, Invest 97L was centered near 8.0°N 36.0°W. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1009 mb. 97L is a tropical wave with a large area of disturbed weather that is beginning to show signs of organization. The NHC currently gives 97L a 20 percent chance of development within 48 hours and a 40 percent chance within five days. Considering recent model trends, I’d place these chances slightly higher. The 12z GFS, ECMWF, and UKMET all developed 97L into at least a weak tropical cyclone by the time it approaches the Lesser Antilles, around late Friday. 97L is a tricky disturbance to forecast, as the model guidance has been showing drastically different solutions. Some earlier GFS runs have developed 97L into a hurricane over the eastern Caribbean, and the 12z HWRF and HMON runs also showed this occurring. However, I have some major doubts in this happening. The HWRF and HMON models typically struggle with tropical waves in the deep tropics that have not developed a well-defined circulation, and often develop systems way too strong. The 18z GFS-based SHIPS guidance suggests that sea surface temperatures will be warmer than 27°C (80.6°F), along with 700-500 mb relative humidity values over 70 percent and deep-layer wind shear less than 15 knots. Although this appears to be a favorable environment, the SHIPS model also suggested that 97L’s forward speed could increase to greater than 20 knots (25 mph), which suggests that 97L will likely struggle to develop and maintain a well-defined circulation if it is not a strong tropical cyclone by the time it approaches the Lesser Antilles. This scenario is reflected on the ECMWF model, which briefly develops 97L into a weak tropical storm on Thursday east of the Lesser Antilles before degenerating it into an open wave before it enters the Caribbean Sea. Considering climatology and the fast forward speed that 97L will likely struggle with, the ECMWF scenario seems quite reasonable. Hurricanes in the eastern Caribbean Sea prior to August are quite rare, with the most recent occurrence being Hurricane Emily during the extreme 2005 Atlantic hurricane season.