Flooding has already been reported in parts of northern Mexico, and another inch or two of rain is likely. The first showers from Potential Tropical Cyclone 4, or PTC4, were also pouring ashore.
Tropical storm warnings are in effect from Boca de Catan, Mexico to Port Mansfield, Texas.
Although the coastal effects of PTC4 should subside as they dissipate late Sunday or Monday, its real impact will not occur until the middle of next week. That’s when heavy rains, accumulating in some places to half a foot or more, could blossom over central Texas, southern Oklahoma and Arkansas.
Much of Texas needs precipitation. The Lone Star State has been plagued by drought lately, with more than 26% of Texas facing “exceptional” high-profile drought, according to the US Drought Monitor.
As of 1 p.m. Eastern on Saturday, PTC4 was still a tropical depression in the Bay of Campeche. The reasons for this designation are purely technical, as the impacts will remain the same.
PTC4 appeared nominally impressive on the infrared satellite, with an obvious vortex signifying mid-level rotation. On the surface, however, Hurricane Hunter reconnaissance aircraft were repeatedly unable to locate a consistent low-altitude circulation center. This means that there is not a single well-defined central vortex, which precludes classification of PTC4 as a tropical storm. Subsequently, she cannot deserve the name Danielle.
Otherwise, heavy shower and thunderstorm activity is evident, and radar indicates a splash of heavy showers approaching the coast. The storm also displays healthy flow aloft, or the exhaust of “spent” air at high altitudes. This is where the storm exhales air from which it has already extracted heat and energy. The longer he exhales, the more warm, humid air he can absorb from below. This promotes its maintenance or intensification.
PTC4 is out of clock. It still has a few hours left before making landfall, and its chances of becoming a tropical storm are diminishing. This won’t change the actual impacts, however.
Isolated to widely scattered heavy showers will pivot ashore in southern Texas and northern Tamaulipas throughout this evening when the center of circulation is expected to land. Because the system is poorly organized, there are no well-structured and unbroken spiral rain bands. Instead, it’s also struggling with some mid-level dry air over the northern half of the storm, reducing precipitation coverage. This will reduce overall amounts to an inch or two, but not much more – at least in South Texas.
Gale winds gusting to over 30 mph are also expected, and a slight coastal push to about a foot deep is expected. Impacts should be minimal.
The storm is expected to disintegrate by noon Monday.
Residual moisture to fuel Texas-sized downpours
Thereafter, the exceptional tropical humidity carried north by PTC4 will remain in place over Texas. A new system – a surface low forming along a locked stationary front near the Red River or Oklahoma border – will draw in this moisture, bringing heavy rainy days.
By mid-week, some locations north of Dallas and south of Oklahoma City, including along Interstates 35 and 287, could see six inches or more of precipitation. This will significantly reduce the existing deficit in this region.
Texas is desperate for precipitation as evidenced by the driest conditions at this point.
Unfortunately, weak PTC4 will not provide what is needed in northeastern Mexico, which is experiencing one of its worst droughts in decades. Reservoirs supplying water to the Monterrey metropolitan area, home to more than 5 million people, have dried up. Tropical cyclones play a critical role in the water supply of northern Mexico and can contribute up to 50 percent summer precipitation in some areas, helping to replenish dried up reservoirs. But as the Atlantic hurricane season got off to a slow start, much of the region, particularly the state of Nuevo Leon, has yet to see significant rainfall.