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Hurricane Larry Forecast Discussion Number 16
2021-09-04 16:59:11| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sat Sep 04 2021 000 WTNT42 KNHC 041459 TCDAT2 Hurricane Larry Discussion Number 16 NWS National Hurricane Center Miami FL AL122021 1100 AM AST Sat Sep 04 2021 Overnight and this morning, Larry appears to have gone through a rather quick eyewall replacement cycle (ERC). The most recent 1000 UTC GMI microwave pass suggests that Larry now has a much larger eye and surrounding eyewall, with less evidence of concentric bands as noted yesterday. On geostationary satellite the larger eye is also becoming apparent on visible and infrared channels, though some left over inner eyewall debris remains. Consistent with the larger eye, an ASCAT-B pass received at 1226 UTC indicated that the 34-, 50-, and 64-kt wind radii have expanded with Larry this morning. While the most recent SAB and TAFB subjective Dvorak intensity estimates have remain at 90 kt and 100 kt respectively, the objective estimates are higher, with an earlier UW-CIMSS SATCON estimate up to 112 kt, though it has recently been adjusted lower. With the eye beginning to clear out on the most recent satellite images, I am favoring the higher objective estimates, bringing Larry up to 110 kt for this advisory. Larry's track has remained fairly steady toward the west-northwest, but just a touch slower and more poleward with the latest estimated motion at 300/13 kt. This west-northwest motion is expected to continue for the next several days with only a very gradual poleward bend as Larry remains positioned to the south of an expansive mid-level ridge extending westward ahead of Larry's expected path. As has been the case the last several days, the track guidance is in excellent agreement over the next 36-48 hours with more spread becoming apparent thereafter. As discussed yesterday, the increase in spread in the latter portion of the forecast appears to be related to how much mid-level ridging stays north of Larry. The ECMWF and its ensembles maintain more ridging that results in a slower and more westward track, while the GFS and its ensembles place more ridging east of Larry that results in a faster more eastward track. The UKMET favors a solution closer to the ECMWF while the Canadian favors a solution closer to the GFS. For now, the latest NHC track has elected to remain close to the HFIP corrected consensus approach (HCCA) which slightly favors the ECMWF solution over the GFS. This latest track forecast is quite similar to the previous one, but just a touch slower. Based on this forecast, Larry will continue moving across the central Atlantic in the coming days, and be approaching the latitude of Bermuda by the end of the forecast period. Conditions continue to remain favorable for additional intensification over the next few days, with vertical wind shear remaining under 10 kts, sea-surface temperatures gradually increasing, and mid-level relatively humidity staying fairly moist. However, by 48 hours, Larry will be impinging on the eastern edge of a large upper-level mid-oceanic trough, which could result in an increase in westerly vertical wind shear over the hurricane. However, the models handle Larry's interaction with this synoptic feature differently. The GFS suggests this upper-level trough will fracture to the west fairly quickly, keeping a more favorable upper-level pattern over Larry, while the ECMWF has a stronger trough that takes longer to give way to Larry's upper-level outflow, providing more westerly shear over the hurricane. Additional eyewall replacement cycles are also possible in the coming days, which could result in additional intensity fluctuations that are challenging to predict ahead of time. For now, the latest NHC intensity forecast keeps Larry intensifying over the next 24-36 hours, with only a very gradual decay thereafter due to the somewhat less favorable dynamical environment. The latest intensity forecast remains on the high end of the guidance, noting that there still remain higher outliers making Larry stronger than the 125 kt peak intensity (HAFS-B, COAMPS-TC). Regardless of the details, Larry is expected to remain a large major hurricane through the forecast period. Significant ocean swells generated by Larry's growing wind field are expected to reach the Lesser Antilles tomorrow, and then spread westward to portions of the Greater Antilles, the Bahamas, and Bermuda on Monday and Tuesday. These swells could cause life-threatening rip currents and high surf conditions. Large swells are also likely to spread to the east coast of the United States by midweek. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 16.8N 45.8W 110 KT 125 MPH 12H 05/0000Z 17.7N 47.5W 115 KT 130 MPH 24H 05/1200Z 19.1N 49.6W 120 KT 140 MPH 36H 06/0000Z 20.3N 51.5W 125 KT 145 MPH 48H 06/1200Z 21.5N 53.2W 120 KT 140 MPH 60H 07/0000Z 22.6N 54.8W 120 KT 140 MPH 72H 07/1200Z 23.8N 56.4W 115 KT 130 MPH 96H 08/1200Z 27.0N 59.4W 110 KT 125 MPH 120H 09/1200Z 31.6N 62.0W 100 KT 115 MPH $$ Forecaster Papin
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