bitter cold, miserable, dreary
淒 centers on a harsh, penetrating cold that makes one feel miserable and dreary, like a bitter chill that seeps into the spirit.
淒 combines the water radical 氵 with 妻, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with cold, wet conditions.
The water radical 氵 suggests dampness, and 妻 (wife) can be imagined as a person shivering in the cold. Picture a wife standing in freezing water, her misery and the bitter cold combining into a dreary scene.
For セイ, imagine the bitter cold making you say 'say' through chattering teeth: 'say' -> セイ, as you try to speak in the miserable, dreary weather.