000 WTNT45 KNHC 182042 TCDAT5 Hurricane Ernesto Discussion Number 29 NWS National Hurricane Center Miami FL AL052024 500 PM AST Sun Aug 18 2024 The structure of Ernesto this afternoon has continued to improve, with a more distinct eye becoming apparent on recent visible and infrared satellite images. This improving inner-core structure is also exhibited in a 1808 UTC GMI microwave pass that also showed a closed cyan ring on the 37-GHz color composite channel, which could be a harbinger for more significant intensification. While subjective Dvorak estimates have not increased much this afternoon, the objective intensity values now range from 60-69 kt and so the initial intensity was raised to 65 kt, making Ernesto a hurricane again. Ernesto's wind field is a bit smaller than yesterday, as indicated by a helpful set of scatterometer passes over Ernesto that were useful to adjust the 34- and 50-kt wind radii earlier today. With the improving inner-core structure, Ernesto is looking increasingly likely to take advantage of the favorable short-term conditions until the hurricane reaches the northern extent of the Gulf Stream at around 40 N. The raw output form the hurricane-regional model guidance now all show an overnight or Monday morning peak intensity of 75-kt or higher in the next 12-24 h, and the latest NHC intensity forecast now shows a bit more intensification overnight. However, Ernesto will quickly move over cooler ocean waters just after 12 h and weakening will likely be well underway by tomorrow afternoon. Shear is also forecast to increase after that time as well, and my best guess at the timing of extratropical transition, diagnosed by FSU cyclone-phase space diagrams and GFS/EC simulated satellite imagery, is shortly after 36 h on Tuesday morning as Ernesto passes just southeast of Newfoundland. The NHC intensity forecast is on the upper-end of the interpolated guidance aids in 12 h, but falls back to the multi-model intensity mean towards the end of its lifespan in 60-h where the cyclone will open up into a trough over the central North Atlantic. Ernesto continues its gradual acceleration north-northeast, estimated now at 020/15-kt. A further increase in forward motion with a turn more northeastward is anticipated over the next 24-36 h as Ernesto becomes caught up in the flow between a large deep-layer trough over the eastern U.S. and a subtropical ridge centered to the hurricane's southeast. A turn more east-northeastward is expected thereafter before the cyclone becomes absorbed by a larger extratropical cyclone located further north between Greenland and Iceland. The track guidance this cycle remains tightly clustered and pretty close to the prior forecast track, and only slight track adjustments were made this cycle. On this track, Ernesto should make its closest approach to Newfoundland just to the southeast early Tuesday morning, with the bulk of the cyclone's wind field staying offshore of the Canadian Provence. Key Messages: 1. Even though Ernesto is forecast to remain well offshore of the U.S. East Coast, swells generated by the hurricane will continue to affect the area through the early part of this week. Beach goers should be aware that there is a significant risk of life-threatening surf and rip currents, and should stay out of the water if advised by lifeguards. Surf and rip currents are also possible on the Bahamas, Bermuda, and Atlantic Canada during the next few days. 2. Ernesto could bring wind, wave, and rain impacts to portions of southeastern Newfoundland Monday night into Tuesday morning. Breaking waves could bring the possibility of coastal flooding, particularly along southwest-facing shorelines from Bunin east to Avalon regions. For additional impact specific information, please see statements issued by the Canadian Hurricane Centre. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 37.1N 62.3W 65 KT 75 MPH 12H 19/0600Z 39.2N 60.9W 75 KT 85 MPH 24H 19/1800Z 42.6N 57.1W 70 KT 80 MPH 36H 20/0600Z 46.1N 50.7W 55 KT 65 MPH 48H 20/1800Z 48.9N 41.3W 45 KT 50 MPH...POST-TROP/EXTRATROP 60H 21/0600Z 51.0N 29.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 21/1800Z...DISSIPATED $$ Forecaster Papin