Last year: 6th
Captain: Jeetan Patel
Coach: Jim Troughton
Overseas players: Ashton Agar, Jeetan Patel
In a nutshell: Birmingham were one of the heaviest scorers in the Blast last year, but they will have to succeed this time without contributions from two New Zealanders, Colin de Grandhomme and Grant Elliott, who have both moved on. Ashton Agar will provide spin support for the admirable Jeetan Patel in the middle overs and if Olly Stone stays fit his pace bowling will add a cutting edge. Michael Burgess' arrival from Sussex should add necessary aggression to the batting.
Star: It is no exaggeration to suggest that Patel stands alongside Allan Donald as Warwickshire's greatest overseas player. This year he also has the responsibility of skippering a side in transition, having taken over from Elliott, his fellow Kiwi, who has retired.
One to watch: Matt Lamb is an academy product whose first-team opportunities have been limited but he could make a major impact in a side a little light on batting matchwinners.
Verdict: No home Finals Day joy this year for Birmingham
Last year: 7th
Captain: Billy Godleman
Coach: Dominic Cork
Overseas players: Logan van Beek
In a nutshell: Derbyshire have been ill-served by planned Australian overseas signings, losing both Kane Richardson and Billy Stanlake. That leaves Logan van Beek, who has played only eight T20 internationals for the Netherlands, fulfilling the overseas role. After a couple of ambitious seasons under the management due of Kim Barnett and John Wright, it is hard to see much joy for Dominic Cork in his first season as coach. Darren Stevens, who has won the tournament with Leicestershire and Kent, fills in, at 43, on a season-long loan from Kent.
Star: Derbyshire will hope that Leus du Plooy, a 24-year-old South African in his first season in English cricket, gets a taste for the Blast; five sixes in a tied Royal London Cup match against Yorkshire in April suggested that he hits a long ball.
One to watch: Billy Godleman's game broadened significantly in the Royal London Cup when he scored 521 runs, including three hundreds, at an average of 74. Can he extend his range even further by making an impact this season in T20?
Verdict: Derbyshire have never reached Finals Day and that is not about to change.
Last year: 2nd, lost to Sussex in QF
Captain: Cameron Bancroft
Coach: James Franklin
Overseas players: Cameron Bancroft, D'Arcy Short
In a nutshell: Durham's improving Championship form has been a welcome prelude to a Blast season where they have realistic hopes of repeating last season's quarter-final place. They surprised some by reaching the quarters in 2018 on one of the more testing batting surfaces in the country when hard running and skilful placement was vital. Crowds are finally rising in the north-east and they are good enough to keep their supporters happy.
Star: D'Arcy Short is one of the most exciting overseas acquisitions in a North Group not exactly brimming with imported talent. An aggressive left-hander, he also adds left-arm legspin to Durham's bowling options.
One to watch: Ben Raine brings fleeting reminders of a more heralded Durham allrounder, Ben Stokes, in his combative approach with bat and ball. His return to the north-east from Leicestershire can help his stock rise.
Verdict: Serious challengers for the quarter-finals.
Last year: 3rd, lost in SF
Captain: Dane Vilas
Coach: Glen Chapple
Overseas players: James Faulkner, Glenn Maxwell
In a nutshell: Lancashire are hanging on the fitness of Liam Livingstone, who is a key component in their batting line-up, but even allowing for that setback, and other injuries in their seam attack, they should be able to assemble a strong challenge. Dane Vilas led Jozi Stars to the inaugural Mzansi Super League title in South Africa and, in his first season in charge at Lancashire, he will hope to make such success a habit.
Star: The World Cup might not have gone to plan for Glenn Maxwell, but Old Trafford crowds should delight in the presence of the unpredictable and potentially explosive Australian.
One to watch: Only Pat Brown took more wickets than Matt Parkinson in 2018 and the legspinner has the potential to become a global T20 star. Warmed up with a career-best Championship return of 6 for 23 against Sussex at Old Trafford.
Verdict: Only injuries will keep them out of the last eight
Last year: 8th
Captain: Colin Ackermann
Coach: Paul Nixon
Overseas players: none
In a nutshell: Leicestershire are another county debilitated by the growing difficulty of attracting overseas players at an affordable price in an era of visa limitations and rival T20 tournaments. Coach Paul Nixon has a good T20 track record but without adequate resources he will struggle to fashion a competitive squad. Leicestershire lost their first five home matches in 2018 and their first task is to avoid a repeat.
Star: Colin Ackermann, this year's captain, offers consistency with the bat and off-spin that is serviceable enough to have brought him 30 T20 wickets.
One to watch: Harry Dearden hit 61 in his solitary T20 appearance and could provide one solution to Leicestershire's shortage of options
Verdict: Doomed to failure
Last year: 9th
Captain: Josh Cobb
Coach: David Ripley
Overseas players: Faheem Ashraf, Dwaine Pretorius
In a nutshell: Josh Cobb became Northants' T20 captain after Alex Wakely called time on his club captaincy and Cobb could supervise a sizeable improvement on last season's unexpected bottom-place finish. The securing of two overseas pace bowlers will sharpen their attack, as will the retention on loan of Matt Coles, who appears to be enjoying his time at Wantage Road. Their 2018 season could prove to be a blip.
Star: Northants will value Pakistan's Faheem Ashraf not just as a fast bowler but as a dangerous late-order hitter who will keep them smiting to the end.
One to watch: Ricardo Vasconcelos' quality in the Championship has been well demonstrated over the past year and he could make the sort of impact that another diminutive left-hander, Ben Duckett, used to provide.
Verdict: Northants can pull off enough shocks to contest a top-four place.
Last year: 4th, lost to Somerset in QF
Captain: Dan Christian
Coach: Peter Moores
Overseas players: Dan Christian
In a nutshell: Which Nottinghamshire is about to turn up - the one that won the Royal London Cup or the one that has been so woeful in the Championship that relegation from Division One already looks assured? A trio of new batting signings, Ben Slater, Joe Clarke and Ben Duckett, need to start delivering on big reputations. Notts have reached the last eight in eight of the last nine years, but the batting stars will have to shine to mask bowling deficiencies.
Star: Alex Hales' self-destructive tendencies lost him a place in England's World Cup squad but he will welcome the opportunity to show that his enforced lay-off hasn't diminished his talents. One of the cleanest white-ball strikers in world cricket, his flying starts will be invaluable.
One to watch: Dan Christian is the Australian captain who must knock the Outlaws into shape, and he must do so without the help of Steven Mullaney, the Championship captain, who misses the early weeks to undergo knee surgery.
Verdict: Runs galore at Trent Bridge but nothing can be taken for granted
Last year: 1st, winners
Captain: Moeen Ali
Coach: Alex Gidman
Overseas players: Martin Guptill, Callum Ferguson
In a nutshell: After losing several quarter-finals, the confidence gained from the 2018 final win over Sussex has encouraged the squad to believe they have enough white-ball pedigree to make a strong defence of their title. Moeen Ali might be captain, and plays in the first two matches, but Brett D'Oliveira will often lead in his absence and needs to stamp his authority on a side that may be a little lacking in the middle order after the departure of Joe Clarke.
Star: Martin Guptill's form will surely pick up after a disappointing World Cup, capped by New Zealand's luckless defeat in the final, and his top-of-the-order forays will be key.
One to watch: Pat Brown faces an interesting second season. He was the leading wicket-taker in 2018 in the Blast, but counties have had an opportunity to study his sleight of hand and come up with responses. It will be harder this time around.
Verdict: A defence of their title may be too much to hope for.
Last year: 5th
Captain: Steve Patterson
Coach: Andrew Gale
Overseas players: Nicholas Pooran
In a nutshell: Tom Kohler-Cadmore steps in unofficially as Yorkshire's T20 captain for the early part of the season while Steve Patterson rests up after a gruelling county season. Yorkshire are hoping for a flying start with the help of their short-term signing, West Indian batsman/keeper Nicholas Pooran and plan to rely more on specialist T20 players, a list which now includes Tim Bresnan, in an attempt to achieve a more explosive style. Dom Bess, on long-term loan from Somerset, and Josh Poysden make up a new spin pairing.
Star: David Willey was the most unfortunate omission from England's World Cup squad, and Yorkshire need him to make an impact with bat (he struck 386 runs at 142.96 last season) and ball if they are to improve on last season's fifth place.
One to watch: Jordan Thompson should get plenty of opportunities as a seam bowling allrounder with T20 potential. After making a T20 debut last year, he has followed up with debuts in the two other county formats this season.
Verdict: Yorkshire have an excellent record batting first at Headingley, but must stop losing soft matches on the road to reach the top four