'Explosive' Delta may be a major hurricane; track uncertainty abounds | WeatherTiger forecast
Delta is intensifying rapidly today as it plows west across the Caribbean Sea, and a late week hurricane threat is coming into focus for the central Gulf Coast.
Theoretically, there are still two tropical systems in play. However, as of the 5 p.m. advisory from the National Hurricane Center, Gamma has weakened to a tropical depression near the northern tip of the Yucatan peninsula. Gamma will likely slide south and inland over the next day or so and dissipate as Delta approaches from the east. Gamma’s only significance is how it will affect the trajectory of Delta, as Gamma itself will have no impacts on the U.S. coastline.
In contrast, Delta is quickly organizing. The 5 p.m. advisory on Delta increases sustained winds to 70 mph, with continued motion due west at about 8 mph. The first reconnaissance aircraft has found significantly lower surface pressures with Delta than estimated earlier, and intense convection now rings the storm’s tightly wrapped central of circulation. This is indicative of rapid intensification, and Delta become a hurricane Monday evening, according to data from a NOAA Hurricane Hunter aircraft.
Small storms like Delta are particularly favored for rapid intensification in supportive environments like the high SSTs and low shear of the western Caribbean. I expect that Delta will reach Category 3 hurricane intensity, at least, before reaching the northern Yucatan peninsula early Wednesday.
Delta’s explosive deepening and Gamma’s disintegration have both short- and long-term implications for track.
More:UPDATE: Tropical Storm Delta forecast to become major hurricane after strengthening to 70 mph
With the upper-level steering more east-to-west for a stronger system, Delta has consistently deviated south of its forecast track Sunday and Monday. Earlier, Delta was supposed to turn northwest into the southern Gulf as it grappled with a more equally matched Gamma on Tuesday and Wednesday; now, the more likely outcome is a path more west-northwestward towards the general vicinity of Cancun as powerful Delta shreds the residual low-level vorticity of Gamma.
Because every model is currently too low with Delta’s actual Monday intensity (and likewise overestimating Gamma), the tightly clustered model consensus for Delta to approach eastern Louisiana on Friday significantly understates the actual uncertainty in the forecast. An upper-level trough moving across Texas Thursday and Friday will turn Delta north and then northeast towards the northern Gulf Coast, but the hurricane could be beginning that turn from a position south and west of where model guidance anticipates.
This means everywhere from Louisiana to the western Florida Panhandle remains at risk of hurricane landfall Friday or Saturday. Delta’s intensity in the Gulf is dependent on how much time (if any) it spends over the Yucatan; conditions in the southern half of the Gulf are relatively favorable for re-strengthening, but water temperatures cool significantly and shear increases in the northern Gulf.
Thus, while a major hurricane landfall is not expected, Delta still is likely to have widespread impacts, particularly near and east of the center.
A long fetch of southerly winds will bring coastal flooding to the central and even northeastern Gulf late in the week. Strong squalls are also possible well east of the center of circulation given the likely structure of the storm on approach to the coast.
It is too early for specific wind and rain forecasts from Delta, but damaging wind impacts are certainly a possibility in the region worst-hit by Sally, including the Mobile, Pensacola, and Destin areas. Probable quick motion at landfall means flooding rainfall is likely to be less of an issue this go-round.
Overall, the situation with Delta is in flux as of Monday afternoon as a cycle of explosive intensification is clearly underway. Expect changes to the forecast in the next day or two as the implications of this strengthening become apparent.
I’ll keep you posted, but it’s time to start preparing for a hurricane on the northern Gulf Coast. Keep watching the skies.
Dr. Ryan Truchelut is chief meteorologist at WeatherTiger, a Tallahassee start-up providing advanced weather and climate analytics, forensic meteorology and expert witness consulting, and agricultural and hurricane forecasting subscription services. For more information, visit us at weathertiger.com or get in touch at ryan@weathertiger.com.
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