For the first time in 2020, there is an Invest (area of investigation) over both the North Atlantic and Eastern Pacific basins. Invest 92L over the central Atlantic could become a short-lived, weak subtropical cyclone during the next two days. Invest 91E is likely to develop into a weak tropical cyclone over the extreme eastern Pacific, but brings a heavy rainfall threat to southern Mexico and central America regardless of development. The next name on the Atlantic naming list is Cristobal, and the next name on the Pacific naming list is Amanda. If 92L develops into a subtropical or tropical storm, it will be the earliest third named storm in Atlantic history, surpassing the record currently held by Tropical Storm Colin in 2016 (June 5).

92L has a chance to become the Atlantic’s earliest third named storm on record

As of 18:00 UTC Friday, Invest 92L was located near 27.6°N 54.7°W. Maximum sustained winds were 30 knots (35 mph), with an estimated minimum pressure of 1015 mb. In their 9:00 a.m. EDT Friday Special Tropical Weather Outlook, the National Hurricane Center (NHC) gave 92L a 50 percent chance of development, both within 48 hours and five days. 92L remains poorly organized with the convective activity removed from the center, which remains broad and elongated. 92L has a narrow window to develop into a weak subtropical cyclone, though it likely does not have enough time to develop into a full-fledged tropical storm. The 12z Friday ECMWF and UKMET model runs show some slight additional development of 92L, while the GFS model keeps 92L weak and disorganized. Sea surface temperatures are a marginal 24-25°C (75.2-77°F), and are only expected to cool further as it moves northward to north-northwestward. The 18z Friday SHIPS model analyzed 45 knots (50 mph) of vertical shear over 92L, though the SHIPS model run predicted shear would decrease to 20-25 knots on Saturday. By late Sunday, sea surface temperatures are expected to quickly drop below 20°C (68°F) while shear increases again, and no development is expected after that time. 92L is not expected to threaten any land areas. However, as noted above, if it develops into a subtropical or tropical storm, it would be the Atlantic’s earliest third named storm on record, and first occurrence of three named storms prior to the official start of the season. This May has been historically active in the Atlantic, with Tropical Storms Arthur and Bertha already having developed. However, pre-season activity in the subtropical Atlantic is not necessarily a harbinger of a hyperactive season. Regardless, our forecast as well as most expert groups are predicting a possibly well-above average season.

91L still likely to become eastern Pacific’s first named storm, but model guidance becoming less aggressive

A Central American Gyre (CAG), a large cyclonic circulation, is developing over Central America. Approximately one to three CAGs develop each year, typically in May-June and September-November. These cyclonic gyres are a common source of tropical cyclogenesis over the eastern Pacific, Gulf of Mexico, and Caribbean Sea early and late in the season. In association with the CAG, a broad area of low pressure – designated Invest 91E – has developed over the eastern Pacific. The NHC gives 91E a 60 percent chance of development within 48 hours, and a 70 percent chance within five days. The five day chances have been reduced slightly since yesterday, and the GFS and ECMWF models do not show any significant development within the next two days. The GFS model does develop a hurricane south of the Gulf of Tehuantepec by the middle of next week, but it is likely that the model is struggling with convective feedback due to the CAG. Predicting genesis with CAGs can be very difficult. If development occurs, 91E may move inland or remain very close to the Pacific Mexican coast. Regardless of development, heavy rainfall and mudslides are a significant threat to Central America and Southern Mexico. Some GEFS and EPS ensembles have suggested the possibility that 91E’s remnants could emerge into the southwestern Gulf of Mexico and redevelop in 5-7 days, but this scenario remains highly uncertain for now.