Spacecoast wrote:"What would you and others guess is the % of runs with a H on it during then?"
I would agree with 60-75%.
https://i.ibb.co/R2PZdHL/ee9.jpg Approx 40% real, 60% false
Source: Halperin et al Oct 2020 "A Comparison of Tropical Cyclone Genesis Forecast Verification from Three
Global Forecast System (GFS)"
GFS 1314: 2013–14 operational configuration
GFS 2015: 2015 GFS configuration
GFS 2016: 2016 GFS configuration
Perhaps I overdid it with guessing 2/3 to 3/4 of GFS runs typically having a H. The reason is looking at 2021. But first here are the 7/31-8/9/2022 GFS runs I know had a H:
1. 8/1 6Z hits S TX after a W Car 8/9 TCG
2. 8/8 6Z forms in SW ATL 8/19 and skirts E coast 8/22-3
3. 8/8 18Z forms MDR 8/24
So, unless one was missed, 2022 was actually a tad quieter than the 10% of 2023 with only 3 of 40 runs (8%) with a H.
Next, I decided to look at a fairly active 2021. Although it had no NS 7/31-8/9, it did have these soon afterward when looking ahead:
-TD Fred form on 8/11 in the NE Caribbean and soon become a TS
-TD Grace form in MDR on 8/13 although not a H til the WCar 8/18
These are the known GFS 7/31-8/9/21 runs with a H (I could have missed a couple of others but hopefully not):
1. 8/1 6Z forms in MDR by 8/11 (Future Grace??)
2. 8/4 18Z 92L
3. 8/6 12Z forms 8/13 Bahamas and hits S FL (Future Fred?)
4. 8/7 0Z 93L MDR 8/11
5. 8/7 6Z 93L forms by 8/10 W MDR
6. 8/7 12Z 93L hits PR 8/13
7. 8/9 0Z 95L Caribbean/GOM
8. 8/9 12Z 95L forms 8/22 hits MX 8/23
So, assuming I missed none and despite it being pretty active when looking ahead, there were still only 8 out of 40 (20%) with GFS hurricanes. Even if missed, say, 5, that would still only make 13 of 40 or ~1/3. So, whereas I still think 10% is quiet for the GFS, it may not be as quiet relative to other seasons as I earlier thought although it is much quieter than it was in July.
