With hurricane season officially underway today in the Atlantic basin, all eyes are on thunderstorms streaming northward across the Gulf of Mexico. This convection is associated with Tropical Storm Beatriz off the coast of Mexico in the East Pacific. Although Beatriz is not a direct threat to the Gulf, tropical moisture from this storm will continue to provide deep convection across the southern Gulf. This moisture will interact with an existing surface trough over the Bay of Campeche providing the potential for low pressure to develop over the weekend, but there are limiting factors for tropical development.
Regardless of tropical development, one key tropical ingredient is present: atmospheric moisture. The higher the moisture content in the atmosphere, the greater chance for deep, persistent convection which furthermore enhances development within tropical systems. Meteorologists analyze a parameter known as PWAT, Precipitable Water, to gauge atmospheric moisture content. NOAA defines PWAT as the “measure of the depth of liquid water at the surface that would result after precipitating all of the water vapor in a vertical column over a given location”. Imagine having a column of water vapor, from Earth’s surface to the top of the atmosphere, and squeezing that column of air until all the water fell out (very similar to wringing out a sponge). The resulting measure of water, calculated in inches, is a good indicator of how much rainfall a region could see.
In the Gulf of Mexico, PWAT values are forecast to climb above 2.0 inches Friday and Saturday. Given the high PWAT values, a meteorologist can determine that deep convection and heavy rainfall will be the primary threats as moisture surges northward.
Despite abundant atmospheric moisture, there is just a low risk of tropical development in the Gulf of Mexico this weekend due to strong wind shear across the region. Strong speed shear hinders development as strong upper-level winds tilt the vortex of the storm, dispersing moisture and heat away the center of circulation. Water temperatures are also slightly below average in the western Gulf for this time of year, which could also inhibit tropical development.
Regardless of tropical development in the Gulf of Mexico this weekend, prolonged heavy rain is anticipated for the Gulf Coast through Wednesday.