By Charlie Hutcherson
As the tropics get rolling in the Northern Hemisphere, the latest El Nino Southern Oscillation (ENSO) outlook shows increasing odds we’ll see La Nina conditions during the peak of the 2020 Atlantic Hurricane Season, which officially began on June 1.
The status of ENSO during the tropical season is the cog that makes a hurricane forecast turn. ENSO’s state is directly correlated to how busy the storm action is in the North Atlantic Ocean.
Forecast: UK + Ireland
El Nino conditions suppress cyclones in the Atlantic while La Nina creates a “safe space” for tropical systems to develop in the Atlantic and the Western Pacific. In contrast, tropical activity is usually reduced in the Eastern Pacific. If La Nina conditions develop this fall, a busy Atlantic hurricane season forecast might be an under call.
But be careful what you wish for. While you may hope for more storms and stronger storms to deliver more surf, they also bring more chances for destructive hurricanes, including major landfalling ones in the US and Caribbean.
We left weak El Nino conditions behind as we moved from spring to summer, entering a neutral phase of ENSO, No El Nino. No La Nina. The UK’s Met Office is in general agreement with the US Climate Prediction Center’s 60 per cent odds those neutral conditions will persist through summer.
Come this fall, we’ve got even odds of neutral conditions continuing — or weak to moderate La Nina conditions developing. With no chance of an El Nino return, there’s nothing significant to suppress Atlantic tropical activity this year. If La Nina conditions arrive, we’ll likely see the opposite effect in the tropics, potentially, even a hyperactive season.
Nothing is ever certain with weather and surf. With the current neutral-ENSO conditions in place, and the forecast calling for neutral or La Nina conditions during the peak months of the season, expectations are for an active to well-above-average Atlantic Hurricane Season.
Logical thinking would say more tropical systems, more chances for surf, but while that may be true for the US and Caribbean, Atlantic Lead and tropical weather expert, Mike Watson, says it’s not that simple.
Once a system moves into the Gulf of Mexico or makes landfall on the US East Coast, it’s (usually) of no help to the surf spots in the Northeast Atlantic. A recurving storm that merges with a mid-latitude storm, then intensifies over the northern Atlantic, is the ideal scenario for Europe
“Recurving tropical systems are what we want to see for good tropical surf in the US and in the UK and Europe. Once a system moves into the Gulf of Mexico or makes landfall on the US East Coast, it’s (usually) of no help to the surf spots in the Northeast Atlantic. A recurving storm that merges with a mid-latitude storm, then intensifies over the northern Atlantic, is the ideal scenario for Europe. We were surprised at the mixed data, however, when we looked at the swell records from our analog years (past hurricane seasons with similar climate signals used for comparison).
“In those years, the June, August, and October surf was below normal — July was considerably above normal and September was slightly above. When we dig deeper, we find anomalous high pressure was over the Northeast Atlantic in these years. High pressure means no storms, topical or not. In this pattern, the mid latitude storm track is pushed further north, along with some of the recurving tropical systems. If two systems were able to merge, it was likely too far north to deliver widespread, significant swell to the UK and Europe.”
The climate signals are pretty damn clear, the transition to La Nina has begun. Stronger-than-normal trades over the equator in the eastern half of the Pacific have allowed cooler subsurface waters to rise to the surface. A zone of the Eastern Pacific (El Nino 3.4) is the prime monitoring area used to determine ENSO — colder-than-normal waters indicate La Nina conditions. Some climate models call for the stronger trades over the Western Pacific, along with cooler sea surface temperatures in the Eastern Pacific to continue through early fall, a strong signal for La Nina conditions during the statistical peak of Atlantic hurricane action. Fire meets tinder.
With El Nino out of the picture, any hurricane expert worth their weight in sandbags knows we’re in for at least an average season in the tropics
With El Nino out of the picture, any hurricane expert worth their weight in sandbags knows we’re in for at least an average season in the tropics — and nearly all notable sources call for above-average storm activity this year. The UK Met Office released one of the more conservative outlooks in late May, giving the most likely season outcome at 13 named storms and seven hurricanes.
Two of the world’s leading cyclone prognosticators, the US’ NOAA and the Colorado State’s Tropical Weather and Climate Research, call for up to 19 named storms and six to 10 hurricanes. An average year has 12 named storms and six hurricanes. We already named four tropical storms (Arthur, Bertha, Cristobal, and Dolly), three of which delivered surf to the US by the first week of the season — that’s one-third the tally of named storms in a normal year. Colorado State also predicts a 50% increase in Accumulated Cyclone Energy (predicted ACE 160, average 106) plus a greater-than-normal chance we’ll have a major hurricane make landfall in the US or Caribbean. The Met Office stays lower once again, calling for an ACE of 110, or slightly above average.
A strong La Nina provides the most certainty of a busy season, but any La Nina conditions in place during hurricane season are favourable for development in the Atlantic tropics.
Under similar climate conditions in years past, we’ve had the two most active hurricane seasons in recorded history, 2005 and 1995, the latter of which produced one of the longest runs of good summer surf ever seen on the US East Coast. The active summer of ’95 didn’t translate to pumping surf on this side of the pond, however.
According to Watson, “during the peak tropical months of 1995, we saw average surf in September and below-average surf in October. And in 2005? Hurricane Vince made landfall as a tropical depression in southern Spain, a record, first-ever event.”
Cover shot by Christian McLeod. A version of this article first appeared on Surfline.