Ua Net Automated Rain Gage Network

HFO’s Ua Net Real-Time Rain Gage Network

HFO’s Ua Net network of tipping bucket gages includes over 65 sites across the State of Hawaiʻi. The network is managed by HFO’s Hydrologist and maintained by Pacific Region Electronic Technicians. Most of the gages are telemetered via GOES (scheduled and random transmission channels), with a smaller number transmitting data via VHF radio using the ALERT protocol. Redundant workstations running the Datawise software provide forecasters with data alarms at 4 threshold levels. They are 0.25, 0.50, 0.75, and 1.00 in 15-minutes, which translates to 1, 2, 3, and 4 inch per hour rates.

Real-time rainfall data can be helpful with the flash flood warning and flood advisory decision making process, and can provide some lead time for the warnings depending on where the event is occurring. Typical flood advisory rain rates are in the range of 1 to 2 inches per hour. Rates of 3 to 4 inches per hour or more warrant consideration of a flash flood warning, especially if significant rainfall has recently occurred and the intense rain is expected to continue for 30 minutes or more.

In addition to providing forecasters with notifications of heavy rainfall, real-time gage data also serve as a ground truth verification data source for radar based rainfall estimates, and can be used to help adjust biases in the radar based estimates. The bias-adjusted estimates serve as the observational forcing for the National Water Model’s Hawaiʻi domain.