Date: 201306
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: Marginal
Weather elements / visibility: Thunderstorm
Light: Daylight
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Situational Awareness; Time Pressure
Anomaly: ATC Issue All Types; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; Flight Crew Diverted
Contributing factors: Airspace Structure; Human Factors; Procedure; Weather
Primary problem: Weather

Narrative: During departure we received vectors over the north side of the ocean which was in the opposite direction of our filed route. These vectors and the resulting route change resulted in a significantly longer route than originally planned for. This new un-planned routing around weather resulted in the necessity to divert for fuel; due to no available alternate that would allow us to go to our planned destination then to our alternate and still land with 45 minutes of fuel. We confirmed with Dispatch over ACARS and due to the need to actually discuss the situation at XA:36z we used Commercial Radio for a phone patch to get a better idea of the weather situation. AT XA:45Z we declared a fuel emergency due to not being able to complete the flight as planned and the miscommunication with ATC. We were very close to another airport and we had a window of opportunity with the weather that allowed a normal descent; and the other airport would also be in the clear shortly after we diverted allowed for a mostly VFR flight to our planned destination once the severe storms passed over the field. AT XA:50Z we changed our destination to the other airport.The biggest threat with this flight was ATC taking us over a completely different route than our clearance! The filed route provided us with a 'hole in the weather' that would have allowed us to complete the flight without anything more than minor weather deviations typical of IFR flight in the summer. What happened after departure was a complete lack of communication from ATC as why they took us south and almost to the maximum 50 NM from land. I felt that they sent us over the gulf route for traffic purposes that did not have anything to do with weather avoidance. There was no notification that they were going to [have us] deviate from our filed and cleared route while we were on the ground.Now knowing that ATC completely deviating from the route we received is more a possibility I will be more inquisitive on the ground as to there intentions before the wheels are off the ground. I felt that during this flight ATC was always just trying to pass us on to the next Controller and most likely should not have allowed us to take off if they couldn't handle our flight with the flights that were already in the air. This flight was planned very tight on fuel with the load we had. If we had received the longer route from ATC on the ground we could have very easily increased fuel to accommodate and avoid the diversion.




Synopsis: An EMB-145 Captain believed ATC's failure to route them via their filed and cleared route resulted in the need to stop for fuel in order to remain legal to complete their planned flight.