WEATHERAmerica Newsletter, Saturday, June 1, 2024

[Larry Cosgrove]

OVERVIEW

I have a suspicion that the temperatures seen in May are the key to the JJAS (summer trimester) period. The generally cool West vs. hot Central/East alignment may be bolstered by the upcoming monsoon season in the Desert and Intermountain Region. The monsoonal trough favors a conjoined Sonoran + Bermudan ridge complex east of the Continental Divide. But as the ridging ages, weaknesses from mid-August through October will allow approach and landfall of warm-core disturbances of either Cape Verde or Caribbean/Sargasso origin, which is why those living along the Gulf Coast and Atlantic shoreline must be alert for a stronger-than-normal hurricane risk. It is too early to say exactly where, and no amount of assertions from "instant experts" or Index lovers can prove just where a tempest may hit. My forecast numbers remain constant: 18 named storms, 10 hurricanes, and 6 major cyclones roughly between August 15 and Halloween. Very warm water temperatures, lowering vertical shear and La Nina climatology do not lie.

The near term, medium range and to some extent the extended period all look cut from the same cloth: the slow build of the conjoined subtropical high and relocation to the Gulf Coast (eventually into the Corn Belt and the Virginias). The trough and upper low established across the Upper Midwest/Great Lakes is a deterrent to brutal heat, and indeed could increase severe thunderstorm potential from the Dakotas to the interior Northeast. Whatever convection that occurs in Texas or the Deep South will likely be of the pulse/diurnal type, with temperatures remaining above normal and very high relative humidity the normal between now and June 11. But look for a hotter realm to edge into the Eastern Seaboard, thanks to the Bermuda portion of the subtropical high.