The 2019 Atlantic hurricane season officially starts today, and right on schedule, we are monitoring an area of low pressure over the Bay of Campeche for tropical development. It has been designated Invest 91L, and has a medium chance of development within the next 48 hours. If 91L becomes a tropical storm, it would be named Barry. The average second named storm in the Atlantic basin does not form until August 1, so if 91L develops, it will be well ahead of schedule. Interests along the western Gulf Coast of Mexico and Southern Texas should monitor the progress of 91L.

As of 18:00 UTC Saturday June 1, Invest 91L was centered near 19.7°N 94.0°W. Maximum sustained winds were 20 knots (25 mph), with an estimated minimum pressure of 1008 mb. Invest 91L is associated with a Central American Gyre (CAG), and remains broad and poorly organized at this time. However, environmental conditions are expected to remain conducive for development for the next couple of days as long as 91L remains over water. Based on the 18z Saturday SHIPS model, wind shear is expected to remain less than 10 knots in the Bay of Campeche, which would favor development. Sea surface temperatures are also very warm, near 29°C (84.2°F). An upper-level anticyclone is currently present near 91L, which is reducing wind shear and making the environment more favorable. A recent ASCAT pass captured 91L, and the circulation remains broad and not yet well-defined. In addition, convective cloud tops have warmed this afternoon. This is not a surprise, however, as 91L is still a developing system and convection typically wanes in the afternoon and evening for developing systems due to the diurnal cycle. Given the favorable conditions, we will likely see a convective burst tonight, and 91L will likely be better organized this time tomorrow as long as it does not move inland into Mexico sooner than expected. The curvature of the Bay of Campeche coastline often allows tropical cyclones to spin up, and 91L could be heading that way. The National Hurricane Center (NHC) gives 91L a 60 percent chance of development, both within 48 hours and five days.

The 12z Saturday GFS and UKMET models do not show significant development with 91L. However, the 12z Saturday ECMWF model run developed 91L into a small tropical storm, making landfall in northern Mexico. It appears likely that 91L will turn to the north on Monday, which could give it more time over water. The timing of the northward turn is critical. If it occurs sooner, 91L could move inland without developing. If it occurs later, 91L will likely develop into a tropical storm. If the northward turn occurs later, that will also likely result in more rainfall in both the Gulf coast of Mexico and Southern Texas. Even if 91L remains offshore by the middle of next week, 91L is expected to move away from the upper-level anticyclone, which would likely lead to increased wind shear and slower development. I will be back with an update on 91L tomorrow.