Steve: It seems to me that climate scientists should rely less on the poor ability of models to represent hurricanes and focus on the ability of models to represent conditions under which hurricane strengthen and weaken. Let's create a database from the historical record for the probability that a category X hurricane or tropical storm in SST Y will strengthen or weaken at a particular longitude and latitude over the next 12 hours. Now let's add some measure of wind sheer to the analysis. What other factors are important? Forward velocity? (Strong winds churn up deeper, colder water and apparently limit maximum hurricane strength.) Patches of drier air?. Now that we know what's important, how well do models predict what is important: SST, wind sheer, etc. Do we think models will do a decent job of projecting changes in these factors?
Commenting on the rapidly intensifying Category 5 hurricane that hit Acapulco (Otis), my weather app said that increases in rapid intensification are caused by climate change and referenced Klotzbach (2021) "Trends in Global Tropical Cyclone Activity: 1990–2021". Unfortunately, although I vaguely remember you commenting on the paper when you returned to your blog, there is a lot I didn't retain.
This study investigates global tropical cyclone (TC) activity trends from 1990 to 2021, a period marked by largely consistent observational platforms. Several global TC metrics have decreased during this period, with significant decreases in hurricane numbers and Accumulated Cyclone Energy (ACE). Most of this decrease has been driven by significant downward trends in the western North Pacific. Globally, short-lived named storms, 24-hr intensification events of ≥50 kt day−1, and TC-related damage have increased significantly. The increase in short-lived named storms is likely due to technological improvements, while rapidly intensifying TC increases may be fueled by higher potential intensity. Damage increases are largely due to increased coastal assets. The significant decrease in hurricane numbers and global ACE are likely due to the trend toward a more La Niña-like base state from 1990 to 2021, favoring North Atlantic TC activity and suppressing North and South Pacific TC activity.
Figure 5 shows that changes in SST, RH and potential intensity partially co-localize, especially decreases in the central Pacific. However, PI increases a moderated by major increases in temperature at the top of the troposphere (where a hurricane's "heat engine" has its "exhaust port". Sad to say I didn't retain much from this important paper, especially the Section titled "Large-Scale Drivers of Observed Trends".
In the conclusion of the paper, they write:
"There are several seemingly consistent changes when resolution is increased:
- increased tropical cyclone frequency and seasonal ACE index in the North Atlantic,
- improved capability to represent the spectrum of tropical cyclone intensities, and
- improved distribution of tropical cyclone tracks (and genesis regions)."
I noted on the first point that generating more isn't necessarily good. On the second point this is definitely the case, but quite a way from actual.
In AR6 they have quite an optimistic conclusion about higher resolution models and TCs, but we'll come to that later.
Steve: It seems to me that climate scientists should rely less on the poor ability of models to represent hurricanes and focus on the ability of models to represent conditions under which hurricane strengthen and weaken. Let's create a database from the historical record for the probability that a category X hurricane or tropical storm in SST Y will strengthen or weaken at a particular longitude and latitude over the next 12 hours. Now let's add some measure of wind sheer to the analysis. What other factors are important? Forward velocity? (Strong winds churn up deeper, colder water and apparently limit maximum hurricane strength.) Patches of drier air?. Now that we know what's important, how well do models predict what is important: SST, wind sheer, etc. Do we think models will do a decent job of projecting changes in these factors?
Interesting question, that I hope to answer in due course
Commenting on the rapidly intensifying Category 5 hurricane that hit Acapulco (Otis), my weather app said that increases in rapid intensification are caused by climate change and referenced Klotzbach (2021) "Trends in Global Tropical Cyclone Activity: 1990–2021". Unfortunately, although I vaguely remember you commenting on the paper when you returned to your blog, there is a lot I didn't retain.
This study investigates global tropical cyclone (TC) activity trends from 1990 to 2021, a period marked by largely consistent observational platforms. Several global TC metrics have decreased during this period, with significant decreases in hurricane numbers and Accumulated Cyclone Energy (ACE). Most of this decrease has been driven by significant downward trends in the western North Pacific. Globally, short-lived named storms, 24-hr intensification events of ≥50 kt day−1, and TC-related damage have increased significantly. The increase in short-lived named storms is likely due to technological improvements, while rapidly intensifying TC increases may be fueled by higher potential intensity. Damage increases are largely due to increased coastal assets. The significant decrease in hurricane numbers and global ACE are likely due to the trend toward a more La Niña-like base state from 1990 to 2021, favoring North Atlantic TC activity and suppressing North and South Pacific TC activity.
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL095774
Figure 5 shows that changes in SST, RH and potential intensity partially co-localize, especially decreases in the central Pacific. However, PI increases a moderated by major increases in temperature at the top of the troposphere (where a hurricane's "heat engine" has its "exhaust port". Sad to say I didn't retain much from this important paper, especially the Section titled "Large-Scale Drivers of Observed Trends".
Best wishes