NFIP flood claims are handled by adjusters certified by the NFIP -- The NFIP expects these adjusters to have had more experience with adjusting large claims, and special knowledge about the NFIP flood policy and claims.
The field adjuster for a flood claim has no authority to settle a claim. Despite the fact that NFIP flood adjusters tend to be the most experienced, Congress and the NFIP require that only the NFIP has settlement authority. That authority is delegated to file reviewers located away from the flood, in centralized offices. Field flood adjusters can not write checks, but they can and do forward requests for advances to file reviewers.
Flood claims can take longer to resolve, both because they tend to be large claims, and because of the review requirements of the NFIP.
Damage from flood losses can take a long time to rebuild, particularly when there is a catastrophe which exhausts available labor and supplies for reconstruction.
There is a unique claim appeal process for NFIP flood claims -- that process includes administrative appeals and special time limitations. If you have a claim, you should receive a claims guidebook from your adjuster.
All of the bullet points, above, apply. In addition:
Under the NFIP flood policy, commercial claims for stock, inventory, and furniture/fixtures are reviewed and processed with very strict guidelines for documentation to substantiate ownership and value.
More information is available on some of the policy differences between flood insurance and homeowners insurance. Some of that information also identifies policy distinctions found in commercial and business owner policies.