Unfortunately the KCLX & KLTX radars are not optimally placed for low-level wind estimates.

Fortunately, Invest #91L will pass directly over buoy 41004 & those obs should give us a good idea if the radar identified center is a closed circulation w/ tropical storm force winds. https://twitter.com/pppapin/status/1265578895530758145

I'll keep this as a running thread on Invest #91L as it approaches the SC coast.

Winds at buoy 41004 are up to 31kt at 10m & the max winds on radar are still 30 mins away. This system could very well already be a tropical storm. #SCwx

As of 1040 UTC, buoy 41004 is up to 33kt sustained 10m winds. Assuming the buoy did not sample the highest winds since the highest KCLX inbound velocities passed south of the buoy, Invest #91L likely has tropical storm force winds.

As of 1050 UTC, buoy 41004 recorded 35kt sustained winds at 10m. This likely confirms that Invest 91L is currently a tropical storm. Just waiting for official word from NHC.

Winds at buoy 41004 actually went up further to 37kt at 1102 UTC with the minimum pressure down to 1009-hPa.

Zooming out a bit, Invest #91L has all the classic characteristics of a tropical cyclone with a small but well organized CDO with curved bands. Onshore surface observations on the outer edge of the circulation also suggest a closed vortex exists as well.

NHC has updated their special TWO, increasing the chances of TCG up to 70% with the wording "If development trends continue, then this system is likely to become a tropical storm before it moves inland later
today."

The latest update from buoy 41004 is even more impressive as of 1118 UTC. Latest 1-min avg 10-meter wind is up to 42.7kt.

Sustained winds with Invest #91L might be closer to 45kt! Tropical storm warnings for the SC coastline will likely be necessary ASAP.

And it is official now! @NHC_Atlantic has declared Invest #91L as Tropical Storm #Bertha with 45-mph winds. Set to make landfall in South Carolina in the next few hours.

I'll stop this thread now, but have to say this was a pretty action packed 3 hours! https://twitter.com/NHC_Atlantic/status/1265615747935375361?s=20