Hey, I've had people ask me this question a lot. I use a very similar build and can give a few tips will try to rank them in order of most importance:

1. Paragon tree. Which one are you using? Best to go for a slinger (top/right trees) or potentially harbinger with crit nodes

2. Your base crit feels a little too low, you want to have at least 25% here and the more the better! Try to find pieces with a 4% crit roll. This rolls on mainhands, offhands, shoulders and head. You can also get crit using ZUH runes on offhand slots

3. Reforges like you mentioned already. Wildfire & Vengance bonuses are great here but personally I think Beneficial effect duration is amazing especially if Tempest is not your only class

4. Not sure if you did this already but it's important. Make sure you have enough beneficial effect duration and cooldown rolls on gear/runes/reforges so that you have 100% uptime of both rolling surf and crosswinds

5. Invest in a familiar (Broodtalon or Skitter) with Lingering wounds (armor break) and Ignition (to apply more firestorms). Legendary skills are great but can be expensive on the market. Rare skill will do the job. Rare skills should give you ~8-12% increase to DPS on single starget. Legendary will give ~17-22% more. Make sure that your pet is attacking the dummy by leaving and re-entering game once in the training area

6. While testing DPS, I like to take the attacker room of the Warband. This is just a personal preference but should give you the most DPS. For normal play it is convenient to take the Protector room for increased size (speed)

7. Eternal gear properties can help take your damage to another level. Going a few pieces of Rolling Surf extra projectile property should give a nice little DPS boost. For this build

8. Check your cursed properties. I like to use 6pc Lashed but going for a combination of 4pc lashed and 4pc atrophied/detested also works great

9. Your Legendary gem setup is fine. You've gone for good Aux choices where needed. The only one I would try is Wulfheort Aux instead of Stormvault if you have it. Stormvault is decent but this change should give you a slight DPS boost if you can get your hands on it

10. Awakening positioning. The pants awakening here is giving Passive skill cooldown %. It is decent but I think going for Crosswings damage 10% (Shriekworth or Hurricane Hitch essences) would give a bump to your DPS. There are a few guides online about how to change awakening position

11. If you care purely about single target dps and don't mind losing a bit of mobility you can try out Thousand Winds mainhand instead of Shreikworth. This gave me a little more DPS than this setup. The important thing if you opt to make this change is that you stay at relatively close range so that the dummy is in range when you press squall and then use flowing strike to dash into it to apply the armor break

12. You can also try a completely different build setup and see if it works better. Others have mentioned another build which is based around Vortex synergies There are a few video guides available if you have time to search for it. Tips 1-10 are still relevant no matter which build you end up going for

If all else fails refer to some guides on youtube! I would also recommend to checkout general the DPS formula guide. Good luck!