https://unidata.github.io/python-gallery/examples/HILO_Symbol_Plot.html#sphx-glr-examples-hilo-symbol-plot-py

image.png

def plot_maxmin_points(lon, lat, data, extrema, nsize, symbol, color='k',
plotValue=True, transform=None):
"""
This function will find and plot relative maximum and minimum for a 2D grid. The function
can be used to plot an H for maximum values (e.g., High pressure) and an L for minimum
values (e.g., low pressue). It is best to used filetered data to obtain a synoptic scale
max/min value. The symbol text can be set to a string value and optionally the color of the
symbol and any plotted value can be set with the parameter color
lon = plotting longitude values (2D)
lat = plotting latitude values (2D)
data = 2D data that you wish to plot the max/min symbol placement
extrema = Either a value of max for Maximum Values or min for Minimum Values
nsize = Size of the grid box to filter the max and min values to plot a reasonable number
symbol = String to be placed at location of max/min value
color = String matplotlib colorname to plot the symbol (and numerica value, if plotted)
plot_value = Boolean (True/False) of whether to plot the numeric value of max/min point
The max/min symbol will be plotted on the current axes within the bounding frame
(e.g., clip_on=True)
"""
from scipy.ndimage.filters import maximum_filter, minimum_filter

if (extrema == 'max'):
    data_ext = maximum_filter(data, nsize, mode='nearest')
elif (extrema == 'min'):
    data_ext = minimum_filter(data, nsize, mode='nearest')
else:
    raise ValueError('Value for hilo must be either max or min')

mxy, mxx = np.where(data_ext == data)

for i in range(len(mxy)):
    ax.text(lon[mxy[i], mxx[i]], lat[mxy[i], mxx[i]], symbol, color=color, size=24,
            clip_on=True, horizontalalignment='center', verticalalignment='center',
            transform=transform)
    ax.text(lon[mxy[i], mxx[i]], lat[mxy[i], mxx[i]],
            '\n' + str(np.int(data[mxy[i], mxx[i]])),
            color=color, size=12, clip_on=True, fontweight='bold',
            horizontalalignment='center', verticalalignment='top', transform=transform)

Use definition to plot H/L symbols

plot_maxmin_points(lons, lats, mslp, 'max', 50, symbol='H', color='b', transform=dataproj)
plot_maxmin_points(lons, lats, mslp, 'min', 25, symbol='L', color='r', transform=dataproj)