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Hurricane Teddy Forecast Discussion Number 26
2020-09-18 22:56:47| National Hurricane Center (Atlantic)
Issued at 500 PM AST Fri Sep 18 2020 000 WTNT45 KNHC 182056 TCDAT5 Hurricane Teddy Discussion Number 26 NWS National Hurricane Center Miami FL AL202020 500 PM AST Fri Sep 18 2020 Both NOAA and U.S. Air Force Hurricane Hunter aircraft have been investigating Teddy since this morning. The highest flight level wind measured by the aircraft was 119 kt at 750 mb, which reduces to around 101 kt at the surface. The latest central measured by the aircraft is up 4 mb from the previous advisory, indicating only some slight weakening. Earlier microwave images indicated that an eyewall replacement cycle had been taking place and some drier air had intruded into the southern portion of the circulation, leaving a partial break in the eyewall. This may explain the reason why the aircraft have not been finding winds as strong as they did previously, and in fact found a double wind maxima in the northern portion of the circulation. These eyewall replacement cycles are common in intense tropical cyclones, and oftentimes the systems recover within 12-24 h as long as the environmental conditions support it. Over the past hour or so, the ring of deep convection has appeared less broken and is beginning to expand in size, which could be an indication that the hurricane is recovering from the eyewall replacement. Based on the possibility of some undersampling by the aircraft, the increase of only 4 mb in central pressure, and the latest convective trends, the initial intensity is being lowered only slightly to 110 kt. Teddy continues its long trek northwestward, now at 12 kt. The hurricane is expected to remain on that general course during the next couple of days as it moves on the southwestern periphery of a mid-level ridge. By the end of the weekend, when Teddy will likely be approaching Bermuda, a turn to the north or north-northeast is forecast to occur as a mid- to upper-level trough moves off the northeastern U.S. coast. Early next week, the trough is expected to cut off, causing Teddy to turn slightly to the left and approach Nova Scotia in about 4 days. The models continue to be in good agreement on this scenario, and only small adjustments were made to the previous forecast track. The environment around Teddy will be conducive for maintaining an intense hurricane for the next 24 h or so, as the ocean temperatures will remain warm with low vertical wind shear and a fairly moist atmosphere. After 24 h, the hurricane is forecast to cross cooler waters churned up by Paulette last week. This should cause a slow weakening trend to begin. By Monday night, vertical wind shear is expected to drastically increase ahead of an approaching mid-latitude trough. This should not only weaken Teddy, but begin its transition to a large extratropical cyclone, and that transition should be completed around day 4 of the forecast period. The latest NHC intensity forecast is near or a little above HCCA and IVCN through 24 h, and then trends toward the SHIPS intensity guidance thereafter. Teddy is producing a large area of high seas. The latest maximum seas estimated by TAFB near the core of the hurricane are near 45 feet. Swells from Teddy are spreading far from the center, see Key Messages below. Key Messages: 1. While the center of Teddy is forecast to move east of Bermuda late Sunday or Monday, there is still a risk of strong winds, storm surge, and heavy rainfall on the island, and a Tropical Storm Watch is in effect. 2. Teddy is expected to transition to a powerful post-tropical cyclone as it moves near or over portions of Atlantic Canada early next week, where there is an increasing risk of direct impacts from wind, rain, and storm surge. Residents there should closely monitor the progress of Teddy and updates to the forecast through the weekend. 3. Large swells produced by Teddy are expected to affect portions of the Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, the east coast of the United States, and Atlantic Canada during the next few days. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 23.1N 57.0W 110 KT 125 MPH 12H 19/0600Z 24.5N 58.1W 110 KT 125 MPH 24H 19/1800Z 26.5N 59.9W 110 KT 125 MPH 36H 20/0600Z 28.1N 61.6W 105 KT 120 MPH 48H 20/1800Z 29.7N 62.6W 100 KT 115 MPH 60H 21/0600Z 31.8N 62.5W 95 KT 110 MPH 72H 21/1800Z 35.6N 61.7W 85 KT 100 MPH 96H 22/1800Z 43.2N 62.7W 75 KT 85 MPH...POST-TROP/EXTRATROP 120H 23/1800Z 48.5N 59.3W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto
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