TLDR;
install using conda in a separate environment, then copy the package folder to your pip environment

Why:
If you do not have a fortran compiler, then you can not build the package yourself.

Step1:
Get miniconda3 (https://docs.anaconda.com/free/miniconda/index.html)

Step2:
make a miniconda environment for the same python version as you have in your other python environment.
conda create -n temp python=3.11
and activate it
activate temp

Step3:
install mamba
conda install -c conda-forge mamba

Step4:
install wavespecta using mamba
mamba install -c conda-forge wavespectra

Step5:
Locate the installed folder

Step6:
Copy it to your main python environment.
That means: copy the whole "wavespectra" folder from yourcondadist/libs/site-packages/ to yourmainpython/libs/site-packages

Step7:
Delete your conda stuff, we will not longer need it

Step8:
Go to your main python environment.

Install all wave-spectra requirementes:

pip install click cmocean dask matplotlib numba pandas python-dateutil pyyaml sortedcontainers scipy toolz typing_extensions xarray

Step9:
Keep your fingers crossed and give it a try: