Last week was a wet one as the rainy season officially began in Florida. Another wet week is ahead not only in Florida, but in the Southeast as well. This rain has been record-breaking for cities like Washington, DC, which has seen their longest continuous streak of at least a quarter inch of rainfall broken.
— NWS DC/Baltimore (@NWS_BaltWash) May 20, 2018
All this moisture is thanks to a combination of an upper-level low that’s been sitting over the Gulf Coast plus a strong Bermuda High off the East Coast of the US. These two features have been teaming up to allow for a constant flow of tropical air and moisture from the Caribbean Sea. The upper-low has been the trigger for the rounds of rain that have been moving through the region. While this low pressure in the higher levels of the atmosphere will weaken midweek, it will re-intensify by next weekend, which happens to be Memorial Day Weekend. This will likely bring more heavy rain to the region, especially if a tropical cyclone forms.
On Tuesday, it will be another wet day — no surprise there — with rounds of showers and thunderstorms affecting not only the Southeast but the Ohio River Valley and the Mid-Atlantic as well. There will also be a few showers that affect southern New England during the morning hours as different areas of weak low pressure pass through. The concern for flooding will continue near the Alabama/Georgia border as well as in parts of the Mid-Atlantic, where over an inch of rain may fall.
On Wednesday there won’t be any large-scale features in the atmosphere that will trigger an organized area of rain. Instead, there will be scattered showers and thunderstorms in the Southeast and Mid-Atlantic. The main factor that will allow for these storms to develop will be solar energy from the sun that heat up and destabilize the air mass. Much of Florida may even end up having a dry day due to a slot of drier air move in from the east. Meanwhile to the north, flooding may be a concern in the southern Appalachians Mountains and northern Georgia.
Thursday will also be a dry day, relatively speaking. It will be similar as Wednesday, with hit or miss storms possible in the Southeast up through the Mid-Atlantic. However, Florida will be back in action with an elevated chance for rain. We want to emphasize how with these hit or miss storms, not everyone will deal with the rain. Some towns may end up with a pretty dry week while towns only a few miles away will see rain all day. It’s basically impossible to predict which individual towns see rain and which do not.
Beginning on Friday, some sort of tropical entity may begin to work into the Gulf of Mexico. We don’t know whether this will be a tropical cyclone or not. What we do know is that the upper-level low will restrengthen over the Gulf Coast, and that’s going to allow for an enhancement of the rainfall during the holiday weekend. It may even be a washout due to a new influx of the deep tropical moisture and higher precipitable water values. Precipitable water, by the way, is the measure of how much moisture is available in the atmosphere for the clouds to use as rain. In terms of Friday’s forecast, hit or miss storms are the expectation, at least as for now, across the Southeast. High pressure over the Northeast should keep much of the Mid-Atlantic dry.