fig, ax = plt.subplots()
m = Basemap(ax=ax)
m.drawcoastlines(linewidth=0.4)
m.drawmeridians(np.arange(-180,180,30), linewidth=0, labels=[0,0,0,1], rotation=270)
m.drawparallels(np.arange(-90,90,30), linewidth=0, labels=[1,0,0,0])

x = np.linspace(-180,180,dat.shape[1])
y = np.linspace(-90,90,dat.shape[0])
img = ax.contourf(x, y, dat, hatches=['-'*2, '/'*3, '\\'*3, '+'*2],
                  cmap=plt.cm.gray, extend='both', alpha=0.5)
cbar = fig.colorbar(img, ax=ax, aspect=30, pad=0.05, shrink=0.65)