Extract MSLP and Draw a Track of a tropical cyclone

[Nere Hingpit]

Hello. I am new to wrf and wrf-python and im trying to study how to postprocess a wrf out file for future work. I have sucessfully followed the WRF-python tutorial in Youtube. I am now interested in extracting MSLP and to draw the track of a tropical cyclone. I found some reference but I cant understand it yet. Would someone be able to share their code for this  or provide a useful reference/tips so i can study it? Thank you in advance.

[Bernard Racoma]

Hi Nere,

You may first want to look take a look at the following form of the hypsometric equation

• MSLP=Psfc*exp(g*dz/(R*T))

I personally adapted the script here: http://weather.ou.edu/~criedel/metr2021/plot_wrf.py (look for "plot_surface"),  although I do believe there are many other ways or methods. Take note you can use the wrf.getvar function  to get the relevant variables (i.e. T2, HGT, PSFC) for your calculations. 

As for calculating and then plotting the track of a Tropical Cyclone (TC), there are many ways to go about this. One of the simplest ways is to find the center by locating the most minimum MSLP within your domain (try mslp.where(mslp==mslp.min() ). However, while this is the simplest way, it may get the tracks wrong very fast especially if your cyclone interacts with land and multiple local minimum low pressure areas appear and are detected as minima. Try implementing a windowing method where you only look for the tracks in locations you know where the TC may be. You may also want to start tracking a few hours (or days) in your simulation since the model might still be spinning up in the first few frames, or the TC has not formed yet. 

Once you get the coordinates of your TC's center, you can use matplotlib's line plot.

I hope this helps.

-BA