On Monday afternoon, the National Hurricane Center (NHC) designated an elongated surface low over the Northwestern Caribbean Invest 90L – the first “Invest” of the 2018 Atlantic hurricane season. The NHC gives 90L a near zero percent chance of development during the next 48 hours, but a 40 percent chance of development within five days.

An Invest – short for area of investigation – is an area of disturbed weather being monitored for potential tropical or subtropical development. Invests are numbered from 90 to 99 with a letter at the end for the basin that the invest is located in (in the Atlantic, the letter is L). After Invest 99L, the next invest would be numbered 90L, and numbering would start over.

As of 12:00 UTC Tuesday, Invest 90L was located near 17.5°N 87.1°W, and was moving little. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1009 mb. 90L is currently poorly organized, with some disorganized thunderstorm activity to the east of the broad low. Environmental conditions are expected to remain hostile for the next couple days, but 90L could gradually develop into a sheared tropical or subtropical cyclone this weekend. 90L is currently struggling with wind shear of about 25 knots. Mid-level relative humidity values were about 60 percent, and sea surface temperatures are a warm 29°C (84.2°F). Shear is likely to drop somewhat if 90L emerges into the central Gulf of Mexico, where development may occur. At the same time, 90L will be moving over slightly cooler waters of about 27°C (80.6°F). The environment for 90L is not likely to be conducive for significant development, and it is extremely unlikely that 90L will develop into a hurricane. However, it is definitely possible that 90L could develop into a sheared tropical or subtropical storm with most of the rain and strongest winds east of the center.

The global models are still very unsure about if 90L will even develop and where it will go. The 12Z ECMWF, CMC, and ICON models all predicted that 90L would develop into a tropical or subtropical depression by Sunday. The ECMWF and ICON models are farther west, with a landfall near Louisiana. The ECMWF in particular shows 90L stalling over Louisiana for several days, which could cause significant flooding. However, the ECMWF remains an outlier at this time with the stall. The CMC model is slightly farther east, with a tropical storm making landfall in the Florida Panhandle. However, the 12z GFS and UKMET models predicted that 90L would remain a broad area of low pressure, and would pass over the Florida Peninsula. I think the eventually end up converging into a single solution, and I think a landfall near the Florida Panhandle is most likely if development occurs. It should be stressed that the potential track of this system is still uncertain.

The main threat with this system, regardless of development, will be heavy rainfall – especially east of the center. Residents along the Gulf Coast and Southeastern United States should closely monitor the development of 90L, as it will very likely lead to a wet Memorial Day weekend. Isolated tornadoes may also be possible, especially in the right-front quadrant of the system if development occurs. If a stall materializes as indicated by the ECMWF, then rainfall totals could be even higher. Since wind shear is likely to be strong, strong winds are not expected to be a major threat with 90L.

The Atlantic hurricane season does not officially begin until June 1, but the United States has seen two tropical cyclones make landfall during Memorial Day Weekend: Beryl in 2012 (Georgia), and Bonnie in 2016 (South Carolina). 90L has a chance to be the third. Tropical development in the Gulf of Mexico during the month of May is very rare, with the last subtropical or tropical storm in the region during month of May being an unnamed subtropical storm in 1976. The first name on the Atlantic naming list is Alberto.

I will be back with another post tomorrow. The 2018 Atlantic hurricane season officially begins in only 10 days.