"HAFS - A" Model now available on the Weather IQ Weather Centre

Author: Chris Nitsopoulos

Posted on: Sunday, December 3rd, 2023, 7:47:57 PM

Good Morning Eyewall Pro users, this morning we have added the "HAFS - A" (Hurricane Analysis and Forecasting System) - storm scale model into the "Weather IQ Weather Centre" It might require you to logout and log back in to have access to the model and its parameters. The HAFS-A replaces the previous "hwrf" model. It has a horizontal resolution of 3km and a vertical resolution of 64 levels making it 3 times the horizontal resolution of the best global model, the ECMWF.

What's New?

1. Wind Gusts (knots) - The model now gives us 1 second wind gusts 
2. 3hr precip - Previously the model only gave us accumulated precip - which could be wildly inaccurate - now 3hr precip gives us a much better understanding of where the rain will fall (especially in the first 72 hours or so of the TC's motion), how heavy it will be and when it's likely to fall.
3. Forecast Atmospheric radar (labeled at WIQ as "Forecast Radar") - Gives us an idea of what the TC will look like on a composite reflectivity radar screen in the future - handy for looking at what part of the storm is likely to have some of the deepest and strongest convection.
4. Forecast ground radar - Takes away a lot of the clutter/cloud from the atmospheric radar away from the TC's core and is handy for looking at areas of actual rainfall on the ground away from the cyclone's core. If you're near the cyclone's core - use the atmospheric radar

Is HAFS A Better than the HWRF model?

There is no doubt the hwrf model was a game changer in analysing the small scale scale atmospheric processes that occured inside a Tropical Cyclone. The amount of times it absolutely nailed rapid intensification or rapid weakening of systems was second to none and set this model so far apart from the competition it was playing the game on another level. But the model had significant errors, it was prone to lots of problems which included: 

• Intensifying TC's that looked like dog's breakfast, for no apparent reason into Cat 5's in a day or so.
• Prone to over-intensification of systems in the 3+ day time frame as well.
• Very poor in forecast track of TC's thereby completely misinterpreting future atmospheric conditions in the area. 
• Didn't have a good grasp of Ocean atmospheric coupling - how the oceans effect the heat engine of the TC.
• Didn't 'understand' that the atmosphere around the TC (not just in its circulation) also had a significant role in weakening, strengthening, moving the TC.

So what does the HAFS A do better?

1. Track forecasts - 10-15% global improvement in forecast error scores with a 30% improvement in day 4/5 track forecast error scores in the Pacific Ocean. That 30% value is hugely significant. 
2. Long Term Intensity forecast - On days 4/5 intensity errors had dropped by 30% in the Pacific Ocean basin. 
3. Ocean-Atmosphere-Cyclone Core interactions - The model really excels here with significant increases in its ability to understand and interpret how changes in the ocean, broader scale atmosphere and core dynamics will affect a TC. The hwrf was so focussed on meso-scale processes and core dynamics creating a situtation where the model sometimes "missed the forest because it was looking at the tree". 
4. Fewer false alarms for RI - There's fewer instances of that extreme rapid intensification for no apparent reason. 

So what does the HAFS A do worse?

• Probability of Detection of Rapid Intensification - While there are fewer false alarms for rapid intensification, the model also does miss a few more legitimate instances of rapid intensification. We saw a good example of this in the TC over Vanuatu in November 2023. In general for short term intensity forecasts the model performs slightly worse or simlar to the previous hwrf model. 

My overall thoughts

From what I've seen I believe this is a 'step forward' in the forecasting of Tropical Cyclones. It does concern me that the probability of detection of rapid intensification has dropped because the thing that set this model so far apart from its competitors was its ability to detect RI (something the global models are so poor at it's almost laughable). But I will certainly welcome the track improvements and the far fewer false alarms. In terms of what we offer on the Weather Centre, I'm looking forward to all the new parameters especially radar and wind gusts. 

Find the HAFS A model on your Weather Centre with an "Eyewall Pro" membership at https://wc.weatheriq.com.au 

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