More Hurricanes Than Expected in 2018

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Seasonal forecasts by leading providers indicated 5 hurricanes for the 2018 season. However, we're already to 5 and almost certain to eclipse 6-7 which is normal for a season given Sep. 10 is the halfway point of the tropical cyclone season. One of the reasons for increased number of hurricanes is the failure of EL Nino to develop as indicated by multivariate ENSO index which is a measure of the atmosphere's response to ENSO.

Seasonal forecasts indicated diminished hurricanes due to cooler North Atlantic and evolving El Nino

But North Atlantic warmed and El Nino failed

So season has become more active

Discussion: Remember the seasonal forecasts (including Climate Impact Company) for diminished North Atlantic hurricanes for the 2018 season citing an unusually cool tropical North Atlantic limiting upper ocean heat for development and an evolving El Nino producing westerly shear to inhibit development. During the past 6 weeks or so those conditions change. The North Atlantic tropics warmed to near normal while record warmth emerged off the U.S. East Coast and El Nino which almost developed in MAY/JUN failed and neutral ENSO remained in-place for JUL/AUG/SEP. The result is a somewhat rare presence of 3 hurricanes in the North Atlantic basin right now. As of today the seasonal forecasts of hurricanes and intense hurricanes by leading providers have already occurred.

Tropical StormsHurricanesIntense HurricanesAccumulated Cyclone Energy
As of Sep. 1095141.7
CSU forecast125164
TSR forecast115158
CIC forecast115158

Table 1: A look at the seasonal tropical cyclone activity so far according to the Colorado State University Tropical Cyclone Project compared with seasonal forecasts by CSU, Tropical Storm Risk U.K. and Climate Impact Company. Sep. 11 is the mid-point of the tropical cyclone season.

Fig. 1: The 12-week Nino SSTA observation chart indicates steady neutral ENSO continues.

Fig. 2: The monthly multivariate ENSO index (MEI) since last May indicates borderline El Nino earlier this past summer fading back to neutral ENSO in JUL/AUG.

Fig. 3: The East Pacific is TRYING to warm in the equatorial region but for now not enough to cause El Nino to form.

Fig. 4: The North Atlantic tropics warmed during August and remain marginal warm in the western basin while recent tropical events have cooled off the outer North Atlantic. Note record warmth off the East Coast.

Summary: So far 5 hurricanes have formed in the North Atlantic basin and for Sep. 10th the normal total is 3. The North Atlantic environment for tropical cyclone development has clearly improved. The normal number of hurricanes in the North Atlantic for a given season is 6-7. Based on observing 5 hurricanes at the midpoint of the season it’s likely the seasonal total of hurricanes will be unexpectedly above normal.