Patches that seem to be maturing early while the rest of the crop is still green do warrant closer inspection. With all the rainfall in some areas, die-off due to excess moisture could be the prime suspect — but check anyway.
Other possibilities are:
Disease. What appears to be premature ripening of a larger magnitude will usually be disease related. Clubroot will often be in patches and serious levels of sclerotinia stem rot (stem rot has begun), blackleg or root rot can be in patches or across a field. Even if you are growing varieties resistant to blackleg and clubroot, check these patches. Genetic resistance can lose its effectiveness, especially when the same variety or similar resistance-source varieties are grown in short rotation on the same field. Diseases to look for when pre-harvest disease scouting. Lesion ID.
Nutrient deficiency. Patches that have run out of nutrients (some of which could be a direct result of excess moisture) can mature earlier than patches with sufficient nutrients.
Insects. Berthas armyworms in a patch will eat down to the pith, which looks blatantly white from the road.