tcwindfields

Parametric 2D wind and pressure fields for tropical cyclone tracks.

Given a TC track (position, intensity, size), tcwindfields produces gridded uwnd, vwnd [m/s] and pres [Pa] fields as an xarray.Dataset ready to save as NetCDF.

Wind model: Chavas, Lin & Emanuel (2015) CLE15, merging the Emanuel & Rotunno (2011) inner-region solution with the Emanuel (2004) outer-region solution.

Pressure model: Holland (1980) radial profile with the Willoughby & Rahn (2004) empirical B parameter.

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Installation

pip install tcwindfields

Dependencies: numpy, scipy, shapely, xarray, pandas, tqdm

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Example: TC Alfred (2025)

import urllib.request, pathlib
import numpy as np
import xarray as xr
import tcwindfields as tcwf

# --- Download IBTrACS (last 3 years, ~10 MB) ---
url  = ("https://www.ncei.noaa.gov/data/international-best-track-archive-for-"
        "climate-stewardship-ibtracs/v04r01/access/netcdf/"
        "IBTrACS.last3years.v04r01.nc")
dest = pathlib.Path("IBTrACS.last3years.v04r01.nc")
if not dest.exists():
    urllib.request.urlretrieve(url, dest)

# --- Extract Alfred ---
ds_ib   = xr.open_dataset(dest)
names   = np.array(ds_ib['name'].values.astype(str))
seasons = np.array(ds_ib['season'].values.astype(int))

idx    = int(np.where((names == 'ALFRED') & (seasons == 2025))[0][0])
ds_tc  = ds_ib.isel(storm=idx)

lons_tc = np.array(ds_tc['lon'])
lats_tc = np.array(ds_tc['lat'])
time_tc = np.array(ds_tc['time'])
vmax_tc = np.array(ds_tc['bom_wind']) / 1.94384   # knots  → m/s
pmin_tc = np.array(ds_tc['bom_pres'])              # hPa
rmax_tc = np.array(ds_tc['bom_rmw'])  * 1.852      # n mi   → km

# Fill RMW gaps with Willoughby & Rahn (2004)
rmax_tc = tcwf.fill_rmax_gaps(rmax_tc, vmax_tc, lats_tc)

# Drop rows with missing position / intensity
valid = ~(np.isnan(lons_tc) | np.isnan(lats_tc)
        | np.isnan(vmax_tc) | np.isnan(pmin_tc))
lons_tc, lats_tc, time_tc = lons_tc[valid], lats_tc[valid], time_tc[valid]
vmax_tc, pmin_tc, rmax_tc = vmax_tc[valid], pmin_tc[valid], rmax_tc[valid]

# Filter to dates of interest
t0 = np.datetime64('2025-02-28T12:00:00')
t1 = np.datetime64('2025-03-08T18:00:00')
mask = (time_tc >= t0) & (time_tc <= t1)
lons_tc, lats_tc, time_tc = lons_tc[mask], lats_tc[mask], time_tc[mask]
vmax_tc, pmin_tc, rmax_tc = vmax_tc[mask], pmin_tc[mask], rmax_tc[mask]

# --- Compute 2D fields ---
lons_grid = np.arange(149.0, 160.0, 0.05)
lats_grid = np.arange(-33.0, -21.0, 0.05)

ds_wnd = tcwf.compute_tc_fields(
    time_tc, lons_tc, lats_tc, vmax_tc, pmin_tc, rmax_tc,
    lons_grid, lats_grid,
    interp_interval='1h',
)
ds_wnd.to_netcdf('Alfred_2025_TC_winds_CLE15.nc')

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tcwf.compute_tc_fields(...)

Main function. Returns an xr.Dataset with dimensions (time, lat, lon).

Input variables:

Parameter	Type	Units	Description
times	np.datetime64 array	—	Track times
lons	float array	degrees E	TC centre longitude
lats	float array	degrees N	TC centre latitude (negative = SH)
vmax	float array	m/s	Maximum surface wind speed
pmin	float array	hPa	Minimum central pressure
rmax	float array	km	Radius of maximum wind
lons_grid	1-D float array	degrees E	Output grid
lats_grid	1-D float array	degrees N	Output grid
interp_interval	str or None	—	e.g. '20min', '1h'; None = no interpolation

Output variables:

uwnd (m/s), vwnd (m/s), pres (Pa).

tcwf.fill_rmax_gaps(rmax_km, vmax_ms, lats)

Fill NaN values in a rmax array using the Willoughby & Rahn (2004) empirical formula. Observed values are kept unchanged.

tcwf.interpolate_track(times, lons, lats, vmax, pmin, rmax, interval='1h')

Interpolate track arrays to a regular time step. Returns a dict with the same keys. Useful for pre-processing before calling compute_tc_fields.

tcwf.input_units()

Print a summary of all required input units and default model parameters.

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References

• Chavas, D. R., Lin, N., & Emanuel, K. (2015). A model for the complete radial structure of the tropical cyclone wind field. Part I: Comparison with observed structure. Journal of the Atmospheric Sciences, 72(9).3647-3662.
• Emanuel, K., & Rotunno, R. (2011). Self-stratification of tropical cyclone outflow. Part I: Implications for storm structure. Journal of the Atmospheric Sciences, 68(10), 2236–2249.
• Emanuel, K. (2004). Tropical cyclone energetics and structure. Atmospheric Turbulence and Mesoscale Meteorology, 8, 165-191.
• Holland, G. J. (1980). An analytic model of the wind and pressure profiles in hurricanes. Monthly Weather Review, 108(8), 1212-1218.
• Willoughby, H. E., & Rahn, M. E. (2004). Parametric representation of the primary hurricane vortex. Part I: Observations and evaluation of the Holland (1980) model. Monthly Weather Review, 132(12), 3033-3048.