"Drought-tolerant" plants always need water their first season. Sometimes even their second season. Many new gardeners kill their brand-new "drought-tolerant" lavender, toyonal, and other plants in California by just planting them, watering them in that first time, and walking away.
"Oh, well...they're 'drought-tolerant,' aren't they?" "Ah...not until they're established."
More to the point of the weigelas--or any new tree/large shrub--is whether they're being deep
-watered like they need. Daily, shallow watering won't encourage a plant to develop the deep roots needed to survive periods of drought. I'd suggest deeper, less frequent watering as well as providing shade during the first season, esp. one as hot as this one is being for the eastern half of the country. Shade cloth, bridal tulle (often on sale at fabric stores like Joann's), or even old sheets will help cut down the solar radiation on the leaves of new trees.
Sunset Zone 17, USDA Zone 9