Sneaky chilly weather into Southern Brazil this morning and Wednesday morning with moderation to follow later this week. Next week, ECM projects a warmer regime across Argentina and Brazil. However, AI 4Cast Net V2 ECM ENS regenerates chilly weather. An important ECM Vs. AI test case for Brazil next week!

A warmer change in the 11-15-day forecast as ECM ENS loses the cool regime into early next week and rewarms much of the U.S. including hot weather extending from California to the Mid-south States. Note the wet arc across Cuba possibly related to a tropical system.

The U.S. population weight CDD forecast reveals the current week as hottest (nationally) of summer 2025 (Fig. 1). Previously, 2 spike hot week regimes were observed ending 6/26 and 7/17. Projected as the 3rd hottest week of summer 2025 is the week ending 8/14.

For now, the North Atlantic tropics environment is mostly not supportive of development. The mid-troposphere relative humidity (RH) for the middle third of July 24, 2025, is very dry across the Caribbean Sea into the Gulf of Mexico which is suppressing development. Sea level pressure anomalies (SLPA) are higher than normal across the northwest Caribbean Sea, Gulf of Mexico, and Bahamas also not supportive of tropical development. +SLPA is also observed in the deep tropics. Another negative factor is the presence of the tropical upper tropospheric trough (TUTT) since June maintained during the middle third of July.