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Hurricane Lorenzo Forecast Discussion Number 29
2019-09-29 16:57:04| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Sep 29 2019 000 WTNT43 KNHC 291456 TCDAT3 Hurricane Lorenzo Discussion Number 29 NWS National Hurricane Center Miami FL AL132019 1100 AM AST Sun Sep 29 2019 Satellite and microwave imagery are indicating that Lorenzo is now weakening. A recent microwave pass showed a broken eyewall as well as dry air in the southwestern quadrant. Over the past hour, the eye has begun to fill in. However, outflow remains excellent and cloud tops remain very cold near the center of the hurricane. A blend of the latest CI values from TAFB and SAB as well as a recent subjective intensity estimate from UW-CIMSS suggest the initial intensity is now 125 kt. Lorenzo is moving north-northeastward at 9 kt through a weakness in the subtropical ridge. A mid-latitude trough will approach Lorenzo from the west in a couple of days. Increasing southwesterly flow ahead of the trough will force the hurricane to turn northeastward and accelerate beginning on Monday. The forecast track confidence is very high through 72 hours, and the new forecast is in good agreement with the tightly clustered consensus guidance and the previous forecast. Beyond 72 hours, the guidance now diverges significantly, likely due to how they are handling the interaction between Lorenzo and a larger extratropical cyclone near Greenland late in the forecast period. The majority of the guidance has shifted to the west by several hundred miles over the past couple of runs. However, there remains significant spread between the operational UKMET/ECMWF which take what's left of Lorenzo toward the British Isles, and the solutions that absorb the cyclone into the larger system well over 1000 miles to the west. Based on the recent shift in the models and the large spread, the official forecast was only adjusted a little to the left and lies well to the right of the consensus aids. Needless to say, the forecast track confidence beyond 72 hours is low at the moment, and may need further adjustments in the next couple of advisories. Lorenzo reached its peak intensity last night, and the intensity guidance is in good agreement that the hurricane will steadily weaken over the next several days due to increasing southwesterly shear, dry air entrainment, and progressively cooler SSTs. The NOAA Hurricane Hunters are still scheduled to investigate Lorenzo later today, and the data they collect should provide a better assessment of the hurricane's intensity and structure. In a few days, Lorenzo will interact with a frontal zone and begin transitioning to an extratropical cyclone. This transition is expected to be complete by 96 hours. It is important to note that although Lorenzo is forecast to weaken through the forecast period, the wind field is expected to expand at the same time, with tropical-storm-force and 50 kt winds forecast to extend over 300 n mi/ 160 n mi respectively from the center in 72 hours. The latest intensity forecast is similar to the previous one, and it is near the HFIP corrected consensus HCCA. Earlier input from the Tropical Analysis and Forecast Branch here at NHC indicates that the large wind field of Lorenzo and its expected faster forward motion in a few days will likely lead to extreme enhancement of the wave field and wave growth over the southeastern portion of the circulation. Key Messages: 1. Lorenzo is a large and powerful hurricane, and its hurricane- and tropical-storm-force wind fields are expected to expand further during the next several days. Regardless of Lorenzo's exact track near the Azores, strong winds are becoming increasingly likely on those islands Tuesday night and Wednesday, and residents there should monitor the progress of the hurricane. Watches could be issued for those islands later today or tonight. 2. Large swells generated by Lorenzo will continue to spread across much of the north Atlantic basin during the next few days. These swells will produce life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 25.9N 44.4W 125 KT 145 MPH 12H 30/0000Z 27.2N 43.9W 115 KT 130 MPH 24H 30/1200Z 28.9N 43.0W 105 KT 120 MPH 36H 01/0000Z 31.0N 41.6W 100 KT 115 MPH 48H 01/1200Z 33.7N 38.9W 95 KT 110 MPH 72H 02/1200Z 42.0N 29.0W 80 KT 90 MPH 96H 03/1200Z 50.0N 18.4W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 04/1200Z 54.9N 11.6W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto
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