B737-800
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Inflight Event / Encounter Fuel Issue; Inflight Event / Encounter Weather / Turbulence
Flight Crew Diverted; Flight Crew Requested ATC Assistance / Clarification
Human Factors; Weather
Weather was deteriorating at [destination with] lightning; thunderstorms; and hail. [We] held short time [and were given] multiple vectors. Decided not to begin approach as weather was becoming significantly worse. Notified ATC of intention to divert to [alternate]. Dispatch concurred [alternate] weather suitable. [Alternate was] not on flight release as an alternate and my fuel estimate for arrival at alternate was very near my comfort level for landing. Declared emergency for minimum fuel as I was not certain of number of other flights diverting to [alternate] and possible delays there from. Approach and landing were uneventful.
B737-800 Captain elected to declare a fuel emergency and divert to an alternate when weather deteriorated at his original destination.