| The landfall was forecast to be around hurricane intensity, sometimes just below it. Here are some of the forecasts: 500 PM EDT Fri Aug 20 2021 48H 22/1800Z 40.8N 72.4W 65 KT 75 MPH 60H 23/0600Z 42.0N 72.8W 45 KT 50 MPH...INLAND 1100 PM EDT Fri Aug 20 2021 36H 22/1200Z 40.2N 72.6W 70 KT 80 MPH 48H 23/0000Z 41.4N 73.4W 50 KT 60 MPH...INLAND 500 AM EDT Sat Aug 21 2021 24H 22/0600Z 38.8N 72.0W 70 KT 80 MPH 36H 22/1800Z 40.9N 72.7W 60 KT 70 MPH...INLAND 1100 AM EDT Sat Aug 21 2021 24H 22/1200Z 39.7N 71.9W 70 KT 80 MPH 36H 23/0000Z 41.3N 72.6W 60 KT 70 MPH...INLAND 500 PM EDT Sat Aug 21 2021 INIT 21/2100Z 36.3N 71.4W 65 KT 75 MPH 24H 22/1800Z 40.8N 72.1W 60 KT 70 MPH 36H 23/0600Z 42.1N 72.4W 40 KT 45 MPH...INLAND 1100 PM EDT Sat Aug 21 2021 INIT 22/0300Z 38.6N 71.0W 65 KT 75 MPH 12H 22/1200Z 40.3N 71.2W 70 KT 80 MPH 24H 23/0000Z 41.9N 71.8W 55 KT 65 MPH...INLAND 500 AM EDT Sun Aug 22 2021 INIT 22/0900Z 40.1N 71.2W 65 KT 75 MPH 12H 22/1800Z 41.5N 71.7W 60 KT 70 MPH...INLAND 1100 AM EDT Sun Aug 22 2021 INIT 22/1500Z 41.1N 71.6W 50 KT 60 MPH 12H 23/0000Z 42.4N 73.2W 35 KT 40 MPH...INLAND I didn't look at each individual discussion, but sometimes they may note if weakening may occur between forecast points. Since the storm was generally forecast to strengthen some over the Gulf Stream and then weaken some before landfall, in some of these instances it might be that the storm was forecast to weaken to below hurricane strength before landfall. For the first 48 hours, forecast points are for every 12 hours. Beyond that, every 24 hours. When there are less forecast points, meaning a bigger gap, more might be going to happen than indicated by the forecast. For some of the earlier forecasts above, there is a big intensity drop in 24 hour period between last point before landfall and the first inland point. The only forecast above to show the storm would be below hurricane strength, if the forecast was exactly correct, was 5pm EDT Saturday, with a forecast point of 70mph offshore. The forecasts kind of rely on where the forecast points are before or after landfall. If a forecast point just happens to be just before landfall, you can see what they might be forecasting for landfall. If it is inland, it will already be weakening and it is harder to tell what they think the landfall intensity will be unless they say it. Here is an archive of the 3 day track: https://www.nhc.noaa.gov/archive/2021/HENRI_graphics.php?product=3day_cone_with_line As for the specific data associated with this storm, its appearance on satellite did make it appear that the storm might be gettering better organized last night at the core. Here is a satellite loop of the overnight: https://re.ssec.wisc.edu/s/21Y9QJ For the 11pm EDT, where they forecast strengthening, it did seem very reasonable for it to go to 80mph. But then recon found that the pressure wasn't falling further. The pressure by sonde didn't rise much before landfall. Final one before landfall was 991mb with 15 knots of wind, so the pressure might have been about 990mb or 989mb. You can see the HDOBs from recon here and see the flight level winds and 10 second SFMR estimates: http://hurricanecity.com/recon/recon.cgi?basin=al&year=2021&storm=Henri&product=hdob While the pressure didn't change much, the winds dropped. At 7:51pm EDT last night, the 30 second flight level wind was 72 knots (83 mph) with 10 second SFMR estimated surface winds of 66 knots (76 mph). For the next mission, the highest SFMR was 48 knots (55 mph) at 6:52am EDT, but that is misleading because the last pass into the northeast quadrant didn't have SFMR values. They might have had issues with the instrument, not sure. In the SE quadrant they had 63 kts (73 mph) at flight level (6:25am EDT) and 16 kts* (18 mph*) noted as suspect. They turned the instrument off for a bit after that and it was intermittent during the flight. For the final mission, the storm was just about to make landfall and they only got to sample a little bit to the east. The highest flight level wind for that mission was 58 knots (67 mph) at 10:41am EDT in the SE quadrant about 51 miles from the center. (and center was about 19 miles from landfall) The highest SFMR winds from that mission were 51 knots (59 mph) and 50 knots (58 mph). The 50 knots was about 11 miles east-northeast of the center as the center was about 8 miles from shore at 11:29am EDT. The 51 knots was at 12:31pm EDT, after they did the final pass through center and that was about 50 miles east of the center, but that value was right next to an island in likely shallow water, so I don't think if it was accurate. (also, the values before and after it were lower and those two were marked suspect) In the 5am EDT NHC discussion this morning they said this: 500 AM EDT Sun Aug 22 2021 "Henri's satellite presentation has remained largely unchanged overnight and early this morning. Deep convection remains over the center and NWS Doppler radar imagery has revealed a convection band that wraps around the circulation forming a loose banding-eye feature. An Air Force Reserve Hurricane Hunter aircraft that has been in the storm for much of the night has reported that the pressure is slightly lower than earlier, around 986 mb, but the flight-level and SFMR winds are not quite as high as before. The initial intensity is maintained at 65 kt for this advisory. The current reconnaissance mission will be in Henri for a few more hours and should provide additional information on the storm's intensity. " From: https://www.nhc.noaa.gov/archive/2021/al08/al082021.discus.026.shtml? Looking at the pattern for that Air Force mission 13 they mention, I could see where they might not have had enough data to downgrade it yet. They do mention the lower SFMR values. The first pass the aircraft did into the center was at 1:16am EDT when it reached the center and then it went into the northeast quadrant. But then they sampled other areas. The next center pass was NW to SE. Then they flew well away to probably sample the extent of the wind field some. The next pass that came into the NE quadrant to the center had them reaching the center at 4:46am EDT. The highest 30 second flight level winds were 61 knots for that pass in the northeast quadrant at 4:34am EDT. Given it takes time to do the advisory, they may have thought they didn't have enough data to lower it at that time. I don't know if they flew through the most intense convection or what any radar velocities might have been. They did mention "Deep convection remains over the center and NWS Doppler radar imagery has revealed a convection band that wraps around the circulation forming a loose banding-eye feature" so they weren't quite ready to go with that it had weakened yet. Based on recon alone though, not counting radar velocities or any actual ground measurements, it seemed like no more than a 60 mph storm at landfall. It just took them some time I guess to review everything. As for going back and forth between tropical storm and hurricane, I would say the confusion might be in the length of time between the last forecast point before landfall and the next one after landfall. The storm was forecast, based on what I recall them saying, to weaken right before landfall perhaps. So it was hard to tell from the forecast points if the weakening was due to the forecast point being inland, the storm weakening due to cooler water perhaps (or something else) or some combination. Since it was so close to hurricane strength, they did need the hurricane warnings. The storm could have just as easily maintained its strength. It ended up weakening more than I thought it would at landfall, especially since last night the core seemed to be getting better organized with deep convection over it. |