Yes Valencia in august is quite calm, many people leaves for holydays even to nearby coastal cities as Cullera, and Valencia is not a destination chosen by spaniards for beach holidays.
Some fallas near or by Plaza de la Reina are relocated to Plaza Ayuntamiento, that's what i have read somewhere.
Weather forecast, some rain/storms on wednesday
El Tiempo. Predicción para los municipios españoles: València (València/Valencia) - Predicción 7 días - Tabla
www.aemet.es
already some heavy storms have damaged a few fallas that were being set up, but not any important one.