From the National Hurricane Center at 4 p.m., Friday, Sept. 18:
Satellite imagery indicates that the circulation of Tropical Depression 22 has become better defined and is now upgraded to Tropical Storm Beta. Although the system is now a tropical storm, satellite imagery shows that the convective pattern is becoming elongated due to the effects of southwesterly vertical wind shear. Visible imagery and scatterometer data showed that the center of Beta was a bit farther east than previously thought, and the initial motion is a somewhat uncertain.
This motion should continue for the next 12-24 h as the storm is steered by a mid- to upper-level trough over Texas and northeastern Mexico. After that time, the trough should weaken and lift out to the northeast, with a mid-level ridge building to the north of the cyclone above an already present low-level ridge.
This ridge should act as a Beta blocker, causing the storm to turn westward toward the western Gulf coast. Between 72-120 h, the mid-level ridge weakens as another mid-latitude trough moves through the central United States and this is expected to cause the storm to slowly recurve toward the northeast.
One change in the track guidance since the previous forecast is that the GFS and ECMWF are a bit faster on the westward motion and show the center near the Texas coast in about 72 hours. The latter part of the new track forecast also shifts westward, but it is still to the east of the GFS/ECMWF.
There is also a chance that Beta could move more northward than forecast before the trough lifts out, which adds an additional touch of uncertainty to the track forecast. So, it is critical that users not focus on the exact forecast track, especially at days 3 to 5. The global models suggest that the current shear may decrease a little after 24 hours when the upper-level trough moves away from Beta.
However, there is a chance of at least some dry air entrainment that would hamper strengthening. The intensity guidance for the most part continues to forecast Beta to reach a peak intensity below hurricane strength, although the latest SHIPS model forecasts a peak intensity near 65 kt. The new intensity forecast is again unchanged in making Beta a hurricane at 60 and 72 hours and it lies at the upper edge of the intensity guidance.