Statistical Model Question

[orion]

I use a worksheet for excel from the site:
http://www.me.utexas.edu/~jensen/ORMM/c ... index.html

Here is an excerpt from the site about the model:

The original forecast models were developed in the late 1970s by Bill Lesso, Professor Emeritus of the University of Texas. They were based on using a Markov process to model the movement of a storm, i.e. the next position only depends on the current position. To develop the probability transition matrices, several hundred historic storms tracks dating back to 1886 were used. The result was a simple, fast computer model that could be run on the newly introduced PC’s. On contract the NHC was using several different models that could be described as ‘aerosol physics’ models consisting of several hundred partial differential equations that, at that time took several hours to run.

The first Lesso models were fast but inconsistent. The models gave either very good forecasts or forecasts so bad that one colleague stated that one were better off spitting upwind! To improve the consistency, a two-step Markov process was introduced and later, the probability transition matrices were changed to be latitude and longitude dependent. Finally, Tom Curry did an extensive analysis of the storms as part of his PhD dissertation research, "Time Series Prediction of Hurricane Landfall", May, 1986, and added a new variation. The current model uses the current position of the storm; the position six hours back and the position of the storm one-day (24 hours) back. Also, he replaced the probability transition matrices with a set of regression equations that are specific for each five-degree band of latitude.

In 2004, Dr. Paul Jensen implemented the model using the Visual Basic for Applications (VBA) macro language for Microsoft EXCEL. This version incorporates a plotting function using maps. Also, the error analysis function is made fully operational. A full description on the use of the model and a file of ‘Historic Hurricanes’ can be found on this website.

I use this in a senior statistics class in high school and we talk about the model and what a purely statistical model does and does not tell us, the students calculate the error, etc. One of my students pointed out that on the hurricanes we have input data for, the output is extremely similar to NHC's A98E.

Are there any model gurus out there that know how 'new' the A98E is and if maybe this is basically it in an excel workbook?? Thanks!

~Jeff

[PurdueWx80]

What a great use of statistics! I wish my high school teachers had been more creative (same goes for college statistics!). That was a great observation made by one of your students, as the '98' is a partially statistical model. It is a working progress, as you can see from the description below....seems to be updated every 5-10 years.

NHC98 - A Statistical-Dynamical Hurricane Track Prediction Model

The NHC98 model is the latest in a series of mixed statistical-dynamic track prediction models. Earlier versions included the statistical models NHC67 and NHC72, and the statistical-dynamical models NHC73, NHC83 and NHC90.

In NHC98, storms are stratified based on their latitude and their current motion, with different equations used for westward and eastward-moving storms. This stratification is used to account for the observation that storms within the easterlies tend to move to the right of the steering flow, while storms within the westerlies tend to move to the left of the steering flow.

South Zone equations are used for storms south of 15oN, and for storms between 15oN and 25oN that are moving to the west or northwest. North Zone equations are used for storms north of 25oN, and for storms between 15oN and 25oN that are moving to the north or northeast.

The NHC98 model produces a forecast track that is a combination of three independent track estimates. The first estimated track is that produced by CLIPER.

The second estimated track is predicted using observed deep layer mean geopotential heights from the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS). Similar to CLIPER, the storm motion is separated into two components. One set of equations is used to predict the along-track movement of the storm at 12-hr intervals out to 120 hr. Another set of equations is used to predict the across-track movement of the storms. Deep-layer mean geopotential heights at two or three locations in the vicinity of the storm are used to represent the mean flow in which the storm is imbedded. Separate equations are used for each time period, but the geopotential height predictors are consistent from one time period to the next in order to avoid abrupt shifts in the predicted storm locations. These two diagrams show the grid points used for the first four time periods for the along track and cross track equations for the South Zone equations. The grids points used in the equations were determined by overlaying the grid shown on historic storm tracks and correlating the deep-layer mean heights at each grid point with the actual storm motion. The grid points that best correlated with storm motion are included in the prediction equations.

The third estimated track is computed similar to the second, except forecast deep-layer mean geopotential heights from the NCEP GFS are used to produce the forecast track. This sample shows the grid points used for the 36 hr, North Zone equations. (Starting with the NHC98 version, the circulation of the tropical cyclone is removed from the numerical analysis before the deep layer mean geopotential heights are determined.)

NHC98 combines the three track estimates (that from CLIPER, that based on the current geopotential height analysis, and that based on the forecast geopotential heights) into an optimum track forecast.

NHC98 is run four times per day. The primary synoptic time NHC98 forecasts (0000 and 1200 UTC) are based on the previous (1800 and 0600 UTC) runs of the NCEP Global Forecast System. A special version, NHC98-LATE, is run at the primary synoptic times using forecasts from the current GFS model run and is available several hours after NHC98.

Reference: Neumann, C. J. and C. J. McAdie, 1991: A revised National Hurricane Center NHC83 Model (NHC90). NOAA Tech. Memo. NWSNHC-44,35 pp.

[orion]

What a great use of statistics! I wish my high school teachers had been more creative (same goes for college statistics!). That was a great observation made by one of your students, as the '98' is a partially statistical model. It is a working progress, as you can see from the description below....seems to be updated every 5-10 years.

Thanks... I have had a blast with it because I get to include the weather in my teaching... and I don't think I have ever seen my stats students so excited. Several went home and downloaded the package onto their computers and came back with all these comparisons and error calculations. I was amazed.

And thanks also for the information! I had found a few sites thru google but not as good as what you sent.

~Jeff

[PurdueWx80]

You're welcome. By the way, I just typed "NHC statistical model" into the Yahoo! search engine and chose the 3rd option. There is actually a decent description of most of the NHC models for all of you out there who have been wondering about them.

http://www.srh.noaa.gov/srh/ssd/nwpmode ... cmodel.htm

[orion]

http://www.srh.noaa.gov/srh/ssd/nwpmode ... cmodel.htm

I had just found this too and bookmarked it and was ready to send it when I read your reply... thanks again! Great site.

~Jeff