quote:Never mind the name: PTC 3 poses a very real threat
The slow-moving system now known as PTC 3 could dump 10” to 20” of rain on parts of the central Gulf Coast this week. Models do not indicate that PTC 3 is likely to become a strong tropical storm or hurricane. Even if it does become Cindy, its sustained winds may never top 50 mph. However, a system like this doesn’t need to reach tropical storm status in order to cause major havoc. This became clear with last year’s “no-name” floods in Louisiana—the nation’s worst disaster of 2016, with more than $10 billion in damage.
Coastal and near-coastal residents from Louisiana to the Florida Panhandle need to be especially watchful of this system. Models have come into somewhat closer agreement on a track toward the north-northwest, toward a weakness in the upper-level flow over the eastern U.S., followed by a slower motion as the steering currents weaken. At that point, the track forecast for PTC 3 becomes more uncertain: it may move around the periphery of a weak upper low in the western Gulf, which could keep it moving close to the Louisiana coast for a prolonged period. The GFS model (see Figure 4 above) has consistently called for one or more pockets of rainfall on the order of 10” to 20” near or to the east of PTC 3’s track.
Bronquote:A serious rain/flood threat for the central Gulf Coast
The much bigger tropical concern in the Atlantic is from a system that hasn’t yet become a depression. Advisories on Potential Tropical Cyclone 3 were launched on Monday afternoon. A Tropical Storm Warning is in effect from Intracoastal City, Louisiana, to the mouth of the Pearl River, and a tropical storm watch from west of Intracoastal City to High Island, Texas (see Figure 3 below). Although the Alabama and Florida Panhandle coasts are not included in the watch, residents there should be aware of the potential for extremely heavy rain even if the potential tropical storm remains well to the west.
(Procedural note: NHC's new Potential Tropical Cyclone advisories, which debuted on Sunday, provide more detailed guidance on systems that are not yet at depression strength but that have a chance of intensifying and bringing tropical storm or hurricane conditions to land areas within 48 hours. Potential tropical cyclones will be assigned numbers as part of the same chronological list that includes tropical depressions. See the related NHC document for more on this new product.)
At 5:00 pm EDT Monday, the poorly structured center of circulation associated with PTC 3 was located over the southeast Gulf of Mexico, about 300 miles south of the mouth of the Mississippi River. Showers and thunderstorms (convection) were blossoming on Monday afternoon across the eastern Gulf ahead of the low, as shown in the satellite image at top. Nearly all of the convection was east of the circulation; this is a common feature of early-season tropical cyclones in the eastern Gulf.
NHC’s official outlook for PTC3 calls for it to become a tropical storm by Tuesday evening, in which case it would be named Cindy. Having two simultaneous tropical storms in June would be very unusual, though not unprecedented. According to Dr. Phil Klotzbach, the Atlantic has seen at least two simultaneous tropical storms in June three times during the 20th century: in 1909, 1959, and 1968.