Will there be more than 8 Atlantic hurricanes by November 30th?
resolved Dec 1
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predicted NO

If Tammy becomes a hurricane and leaves in 7 days... then the base probability of another 2 hurricanes is about ~21%.

Right now only half of the models for Late guidance 18Z show it becoming a hurricane, so conditioning on the 21% above by 50% leaves ~10% which is near the market probability. OFCL doesn't show a hurricane in 5 days (and at best I can assign 47% probability that the forecast is off by -5kt or more at 5 days which is still less than 50% above); but if OFCL does update to show a hurricane I will sell some of NO shares.

bought Ṁ40 of NO

NHC now forecasting Tammy to be a hurricane. Late guidance shows most of the models of it becoming a hurricane, so I assign a probability of Hurricane Tammy being #7 as 67%, pushing up the question to ~14%

bought Ṁ25 of YES

Now NHC is forecasting Tammy to become a hurricane in 48h (Manifold has it at 85%, I put it at least 75%)), so I am betting with some small YES bets with the probability as 17%.

bought Ṁ10 of NO

NO, The likelihood of having more than 8 hurricanes in the Atlantic is low, given the advanced stage of the hurricane season and data from the previous year. The National Oceanic and Atmospheric Administration (NOAA) predicts a maximum of 11 hurricanes for the current season. NOAA's outlook for the 2023 season anticipates 14-21 named storms, 6-11 of which could become hurricanes, with 2-5 potentially reaching major hurricane status. NOAA expresses 70% confidence in these predictions. The historical data from last year also supports the current assessment, making the probability of more than 8 hurricanes in the Atlantic less likely (NOAA, 2023, August 10; 2022, Atlantic Hurricane Season).

(2023, August 10). National Oceanic and Atmospheric Administration.

Also take a look here for last year results (2022, Atlantic Hurricane Season. (n.d.). )

bought Ṁ29 of NO

Still at 6 hurricanes. Based on my own workbook, the cumulative probability is ~ 34.4% for at least 2 more hurricanes (this only counts storms originating in NA basin, and doesn't consider whether the storm crosses basins or which basin it strengthens in). Edit: This actually counts if there was a hurricane present during the time frame (so it's possible the strengthening to hurricane happened prior, in which case it might be over-estimating the probabilities):

predicted NO

@parhizj blah blah

bought Ṁ94 of NO

@will58c3 blah blah? 😦 The market should be much lower... 34% for 8 hurricanes, but for the question it asks for 9 hurricanes... ("more than 8") so it should be closer to 11% for base rates...

predicted NO

@parhizj sry. North Atlantic basin as opposed to Pacific, right? Or opposed to Gulf or Caribbean?

predicted NO

@will58c3 Question title includes "Atlantic".

It doesn't seem to specify North or South but South are very rare.

predicted NO

@ChristopherRandles Atlantic hurricanes include Carribean and Gulf. I was wondering if Atlantic basin means something different (I don't think it does).

predicted NO

@will58c3 No that’s the intended meaning—Atlantic season broadly construed.

predicted NO

@will58c3 Without putting more words in the mouth of the question creator, in best tracks they mark Gulf of Mexico as a sub basin of the Atlantic so I’m assuming that includes the Gulf of Mexico

predicted NO

@parhizj I was just referring to your comment not the title of the market,

predicted NO

@will58c3 Oh, in that case specifically applies to that dataset where Gulf of Mexico is a sub basin, so it is included.

predicted NO

@parhizj yeah i basically share your reaosning and statistics (w/ bit different methodology) 👍 obv there's the africa disturbance now.

At 6 hurricanes just past the peak of the season, and need three more… there is one disturbance that looked like it would become a hurricane but latest GFS from 00Z doesn’t show that anymore (latest NHC outlook from 8AM EDT still has it at 70% though) through the start of October, leaving October and November for 3 more hurricanes. ECMWF extended ACE forecast shows higher than normal energy the first week of October (2nd-9th), and lower than normal energy approaching the middle of October (9th -16th). With El Niño (through JJA at 1.1 and forecast to likely (65%) be above 1.5 for SON) we may see a less active hurricane season going through November.


Of these three years that have the same number of hurricanes so far, one had 8 or less, and two had more than 8 putting the probability using these analogs at 66%. Note that only 2012 of those three years had hurricanes develop in October, so perhaps it should be a bit less?

The CSU forecast from Aug. 3 also had 9 hurricanes forecast.

Given all this I think the market probability of less than 66% is justified at the moment so I won’t bet for now.


bought Ṁ20 of YES

Edit: nevermind, misread.