The Tropical Atlantic's Heating Up (Again)

After a brief cooldown in June, tropical Atlantic waters are on the upswing yet again

The big story going into this hurricane season was the chart-topping warmth throughout the Atlantic Main Development Region – the strip of tropical waters from the Caribbean to Africa where most of our strongest hurricanes get their start later in the season.

The extent of the record ocean heatwave, which began at the beginning of last hurricane season, is truly unprecedented. But last month the Atlantic seemed to blink, with seasonal warmth finally dropping below 2023’s record levels – albeit still historically high.

Unfortunately, the prospects of a return to normalcy – to the days when virtually the entire tropical Atlantic wasn’t at all-time highs – appears short-lived. MDR waters are once again on the upswing and forecasts suggest this next round of warming will persist at least into early August.

Why the June cooldown across the Atlantic?

In truth, Atlantic waters didn’t so much cool in an absolute sense in June, but the departures from seasonal averages declined. By the end of the month, sea surface temperatures across the Atlantic Main Development, while still well above average, were consistently running behind 2023 records for the first time this year, at points even falling behind 2005 and 2010, our other historical frontunners.

The cooldown is mostly linked to a stronger than average dome of high pressure over the northeastern Atlantic called the Azores High – so named for its semi-permanent position over the Azores islands about 1,000 miles west of Portugal.

This stronger-than-average surface high pressure increased the east-to-west flowing trade winds on its southern periphery across the tropical Atlantic. For the first time since March, trade winds in the tropics ticked noticeably above average.

This surge in trade winds – like a refreshing breeze on a warm summer’s day – helped to cool off the Atlantic by mixing up the ocean. Additionally, a significant outbreak of Saharan dust blanketed the Atlantic starting the last few weeks of June, helping veil waters from the intense summer sun. By the end of June, the departure from average in sea surface temperatures across the eastern Atlantic was the lowest since last December.

A reinforcing marine heat wave on the way

The Atlantic warmth is already climbing out of its June hiatus. As the Saharan dust cover naturally fades into August, forecast models show a weakening of the Azores High accompanied by trade winds once again tanking across the main development region.

Zonal (east-to-west) wind anomalies for the last week of July. Warmer colors (positive values) indicate westerly anomalies, or wind anomalies opposite the typical east-to-west flowing trade winds in the deep tropics. The red band indicates much weaker trade winds expected in the weeks ahead, which will help to once again warm up the Atlantic Main Development Region or MDR. Credit: TropicalTidbits.com

This combination of factors should turn up the burner throughout the deep Atlantic just as hurricane season activity ramps up. Already 80% of the Atlantic main development region is at record or near-record warmth for the time of year, so this only adds fuel to an ongoing fire.

Compared to 2005 – once of our most active hurricane seasons on record – sea surface temperatures this summer are in a different league.

Mid-July slumber continues into next week

As we covered in newsletters earlier in the week, the Atlantic is closed for business, at least for the next week or two.

Saharan dust is at its annual peak while dry, sinking air is keeping any organized storminess at bay.