As early October arrives, the North Atlantic basin observed sea surface temperature anomalies (SSTA) remain much warmer than normal. Clearly, the best place for tropical cyclone generation/intensification is the western and northern Caribbean Sea where upper ocean heat is immense. Moderate to strong upper ocean heat is also present in parts of the Gulf of Mexico, East of the Bahamas, and central North Atlantic tropics.

The immediate forecast issues include risk of another Gulf of Mexico tropical cyclone. NOAA/NHC identifies a tropical wave southwest of Jamaica having a 50% chance of tropical cyclone development after 48 hours. The 12Z GFS indicates the system develops slowly and eventually reaches the north/northeast Gulf of Mexico Coast early in the 6-10-day period.

The U.S. week 2-4 outlook features sprawling high pressure across the West and Central U.S. producing a nationally drier and warmer than normal climate through mid-autumn. The Gulf of Mexico may be tropically active (after Helene) otherwise rainfall in the U.S. is sparse.

Hurricane models (HWRF and HMON) initialize the 8AM EDT central pressure at 952-953 MB, so slightly too strong. HWRF takes Helene to a 935 MB/138 mph category-4 major hurricane by 8PM this evening with landfall across the Apalachee Bay area late this evening. HMON is not quite as strong, indicating 941 MB/133 mph category-4 major hurricane at 8PM this evening with landfall shortly after midnight in the Apalachee Bay area.

The southern oscillation index was neutral much of the past 1-2 weeks correlated to easing trade winds. However, +SOI is forecast to re-emerge. The subsurface waters in the equatorial East Pacific have cooled significantly the past 30 days indicating increased energy to fuel La Nina if trade winds become established.

Potential Tropical Cyclone Nine strengthens to a tropical storm by tonight and becomes a hurricane once reaching the southeast Gulf late tomorrow. The HWRF model takes Helene to a strong category-4 major hurricane in the northeast Gulf of Mexico on Thursday just prior to landfall.

During recent years, the (certain) catalyst to a category-4/category-5 major hurricane has been travel of the tropical cyclone across 31C/87F (or warmer) SST. Right now, the SST for the most likely path of Helene is 30C/86F certainly sufficient to fuel a category-3 major hurricane. The SST across the northeast Gulf of Mexico is a scary 0.75C to 1.75C warmer than normal.