La Nina development stalled during the past 10 weeks or so as the subsurface cool waters required to ignite cold ENSO lost half their April intensity. However, during the past 7-10 days, cooling has resumed indicating La Nina development has returned. The Nino34 SSTA has cooled to -0.13C and appears to be trending toward the -0.50C La Nina threshold based on the 30-day change of -0.55C.

The 2024 daily southern oscillation index (SOI) identifies the uncertainty of direction in ENSO phase. Recently, SOI has spiked highly negative albeit for brief periods. The negative phase is an indicator of an El Nino climate. Conversely, a strong positive spike occurred late JUN/early JUL which indicates a strong La Nina climate. The recent spikes are a new SOI character compared to weaker daily SOI observations of MAR/APR/MAY 2024.

Regions of very warm ocean water known as marine heatwaves (MHW) are commonly linked to high pressure in the upper atmosphere which cause a dry and warmer than normal climate. MHW’s are present and quite strong off the U.S. West Coast and south of the Canadian Maritimes.

The month ahead outlook valid for August 2024 identifies above normal temperature risk for the entire U.S. particularly in the Great Basin and central Appalachians. The probabilistic rainfall outlook has increased confidence for a wet pattern in the Gulf States, Florida, and Carolinas. The wet zone is a candidate for land-falling tropical cyclones in August.