Date: 201808
Local time of day: 0001-0600
Location: ZHU.ARTCC, TX
Weather elements / visibility: Thunderstorm
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZHU
ATC / advisory: Center ZHU
Aircraft component: Safety Instrumentation & Information
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural FAR; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft; Human Factors; Weather
Primary problem: Aircraft

Narrative: While deviating south of weather over the Gulf of Mexico we exceeded 162 miles from shore. I notified ATC that we were exercising emergency authority to do so during the duration of the exceedance and advised when back within 162 miles of shore. The flight was otherwise uneventful. Landed without further incident.WSI was inoperative. ATC advised that other aircraft had deviated to the south without problem. Also; our radar does not provide useful information when IMC. The radar look angle was 3 degrees low; and returns would appear and disappear as we tried to avoid the returns being displayed. Having seen during VMC that the radar paints cells that are not a factor (well below) it's difficult to get a good understanding of relevant weather ahead of you. Thus; the radar display must be honored and returns avoided.Make WSI reliability a priority. Update weather radar software to show more relevant information (tops; as in terrain or radar tops maps available elsewhere; but certainly have the ability to see what is at your flight level or not).


Second narrative: Enroute ATC suggested that we fly a heading of 125 degrees to circumnavigate thunderstorms based on what other aircraft had previously done to avoid weather and we accepted the Controller's advice. We found ourselves on the south side of a major line of thunderstorms and it became apparent that our only option to safely skirt the weather was for us to go beyond 162 NM from shore. The Captain advised ATC that we would need to use Captain's authority to exceed 162 NM from shore to navigate around the weather. We were south of ROZZI intersection on a 125 heading at the time we exercised Captain's authority. We safely navigated around the weather and advised ATC at the time we were done deviating under Captain's authority and landed uneventfully.Factors that lead to deviating beyond 162 NM were our inability to get the on-board WiFi to work which would have aided us in seeing the entirety of the line of thunderstorms in real-time. In the future it would be helpful to have better communications with our Dispatcher to work out a better routing well in advance of the weather.

Second callback: Reporter stated their WSI weather datalink system is dependent on the WiFi signal and is only reliable and usable about 30% of the time.

Synopsis: Air carrier flight crew reported they exceeded the 162 mile from shore limit while avoiding thunderstorms in the Gulf of Mexico area and with limited onboard weather information due to Wifi outage.