Dramatic Cooling Gulf of Mexico While North Atlantic Outer Tropics are Very Warm

Fig. 1-2: Daily Gulf of Mexico SSTA (left) and the 30-day change (right).

Fig. 3-4: ECM ENS and GFS OP 15-day percent of normal precipitation forecast across the Gulf.

Discussion: The unusually warm Gulf of Mexico SST of Q1/2023 increased low-level atmospheric moisture that when entrained into mid-latitude synoptic storms, caused excessive rainfall and unusually intense severe weather. However, the increase in southern latitude storm track intensity inspired by transient Pacific MJO episodes in March and April has caused a steady loss of upper ocean heat in the Gulf of Mexico in recent weeks (Fig. 1). The 30-day SSTA change in the Gulf of Mexico is nearly 1C (Fig. 2).

Another transient MJO episode is forecast for May which should favor a cloudy and wet regime in the Gulf of Mexico and produce additional cooling in the Gulf due to diminished sunlight. The ECM ENS identifies the developing stormy trend in the Gulf leading into the middle of May (Fig. 3). Forecast confidence is reasonable, however not a guarantee. Note the GFS ignoring the MJO influence in the Gulf preferring above normal sunlight which rewarms the Gulf (Fig. 4).

Global SSTA models all failed to forecast the April cooling in the Gulf of Mexico and their current very warm SSTA predictions for summertime in the Gulf may be overstated. The SSTA pattern in the Gulf contributes to the potential strength of a tropical cyclone passing through this region.

Meanwhile the SSTA pattern in the main development region (MDR) for hurricanes is the warmest since 2010 for early May (Fig. 5). The tropical North Atlantic (TNA) index which covers the MDR has roared to +1.01C as May 2023 begins. El Nino ahead should hold down tropical cyclone development this year but the very warm SSTA in the eastern North Atlantic tropics and subtropics which may be part of a marine heat wave (MHW) developing off Northwest Africa could cause an over-achieving year in the tropics despite presence of El Nino.

Fig. 5: Tropical North Atlantic index surges to +1.01C, warmest since 2010.