Wicketkeeper-batter Southby fired her second fifty in succession – after a tough start to the campaign – reaching a scintillating 90 not out in 40 degree heat.
Abi Norgrove’s 64 and Amanda-Jade Wellington’s 42 helped underpin Hampshire’s 265, before the spinners provided the finishing touches.
Georgia Redmayne and Abbie Freeborn provided some defiance with half-centuries but Hampshire made it eight wins from 11 to stay four points behind The Blaze.
Maia Bouchier ran opener partner Georgia Adams out and then herself in a frenetic opening five overs, after Hampshire had chosen to bat.
But Norgrove got the innings moving with a flurry of boundaries, with leg side flicks getting particular value in a 42-run stand with Cesca Sweet.
Norgrove, a former England Under-19 captain, started the season with 195 runs across her first three innings but only added another 60 in the following five outings. This was a return to the former form, with taking responsibility for the innings a key tenet of her game.
After Sweet had swung to deep midwicket, Southby entered and took control of the innings. With Norgrove, she put searing heat aside to selflessly run hard between the wickets- the pair running a combined 78 singles in their innings.
The pair put on 81 before Norgrove, who had slowed after reaching a third fifty of the season, skied down the ground.
Naomi Dattani and Nancy Harman also fell in quick succession but Amanda-Jade Wellington matched Southby’s run-a-ball scoring rate in a 74-run stand.
Southby’s One-Day Cup form had been non-existent in the first block but a new pinch-hitting role in the Vitality Blast sparked a half-century against Somerset on 50-over return.
This was a further step-up, and truly demonstrated the improvements in her batting in the past two seasons.
There was touch-play, and neat gap finding, but the more powerful strikes down the ground really stood out – just a lack of time prevented her from reaching a maiden century.
Chasing 266 to win, Warwickshire lost three wickets in the powerplay, as Bex Tyson and Georgia Adams’ tight spin kept the hosts in charge.
Tyson bowled Amu Surenkumar and Sophie Beech before Davina Perrin’s comeback after seven weeks absent with a hamstring injury, was ended with a loopy slice to cover.
Hampshire were on top, but Redmayne and Freeborn began to turn the tide with an 88-run alliance – ticking along at just below the required rate.
Australian Redmayne grabbed her first half-century for the Bears and Freeborn followed her to milestone but things fell away as they lost their last six wickets for 52 runs.
Adams claimed three for 30 to lead her side, with Tyson, Wellington and Poppy Tulloch all picking up two scalps.
