On Tuesday, the National Hurricane Center declared an area over western Caribbean Sea as “Invest 91L.” This designation means that tropical models, or the “spaghetti models,” will be run on this potential tropical cyclone. This invest will also get its own satellite sector so forecasters have the ability to take a better look at this area of disturbed weather through satellite imagery. As of 8am ET Wednesday, Invest 91L is being given a 20% chance for development within the next five days as the enhanced convection moves to the north and west. If the thunderstorms do organize into a tropical cyclone, then it will happen over the Bay of Campeche in the Gulf of Mexico.
Based on this morning’s model guidance, both the ECMWF (European) and GFS (American) models are not liking the idea of the formation of a tropical cyclone. Less than 10% of the ECMWF’s 50 ensemble members develop a tropical depression by the end of this week, and none of the GFS’s 20 ensemble members show any signs of a low pressure forming.
Therefore, we are not concerned about a tropical cyclone forming over the western Gulf of Mexico for now. Even if a cyclone were to form, it would be very weak. This is due to land interactions with Central America and the presence of wind shear, which prevents the development of tropical cyclones.
Name or not, the impacts will be the same. The main threats associated with the plume of deep, tropical moisture that will move up from the western Caribbean Sea to Texas is heavy rain and some flooding. This moisture plume will likely contain record-breaking precipitable water levels, which is a measure of the amount of available moisture in the atmosphere. When these values exceed 2 inches, there is a good chance some areas deal with heavy rain. With this plume we’re tracking, much of eastern Texas and eventually eastern Oklahoma will likely get in on the 2+ inch precipitable water values, and some locations at the Texas Gulf Coast will likely exceed 3 inches during the Sunday into Monday time period.
This moisture plume will be associated with a trough, an elongated area of low pressure, over the western Gulf Coast. This trough will be very slow-moving, allowing for a prolonged period of rain, some of which will be heavy and may cause flooding. One of the saving-graces in this setup is that Texas has been very dry, so the soil should be able to handle this. Portions of the Texas coast — the southern portion in particular — is experiencing a severe drought. A widespread 2 to 4 inches is expected from the Big Bend of Texas through the Texas Gulf Coast. Localized areas will likely record over 6 inches. Based on the latest model guidance projections on the rainfall, the Houston area could be at risk for the heaviest rain. This makes for the concern for some road and river flooding.
Impacts with the thunderstorms associated with Invest 91L will begin on Saturday, as scattered showers and thunderstorms move into southern and eastern portions of the state as well as coastal Louisiana. On Sunday, the heavier, steadier rains will begin to move onshore, especially from southeastern Texas through the western Louisiana coastline. Unfortunately, it will not be the nicest of Father’s Days. By Monday, these heavier rains will expand, leaving much of eastern Texas and even southeastern Oklahoma at risk for heavy, flooding rains. The shower and thunderstorm activity will also become a bit more widespread across the Southern Plains, eastern New Mexico, and Colorado. On Tuesday, much of eastern Texas and Louisiana will dry out as higher pressures move in. To the west, tropical rains will continue across the southern and central Rocky Mountains and portions of the Southern and Central Plains. Heavy rain will remain a concern, especially on the leeward side of the mountains as moisture gets pushed against the rapid increase in elevation. More of the region will experience a drying trend going into Wednesday, although the leeward side of the Rocky Mountains and portions of the Plains will deal with another day of scattered storms.
Now on Thursday, this tropical moisture will finally begin to move out as a storm system from the north expands the moisture all the way toward the Mid-Atlantic. Much of the Plains and Rocky Mountains will be dry by this point in time. The activity will turn to the Ohio River Valley and Mid-Atlantic, where flooding rains will now be possible there. A cold front will then push that moisture and the rain to the Gulf Coast and Southeast on Friday. At the tail-end of this front, which happens to be in the Southern Plains, the scattered shower and thunderstorm activity will remain present. Through Friday, a widespread 1 to 3 inches of rainfall appears to be a good bet across the Southern Plains and surrounding areas due to this onslaught of highly-anomalous moisture.