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Tropical Storm Eta Forecast Discussion Number 6
2020-11-02 03:52:11| National Hurricane Center (Atlantic)
Issued at 1000 PM EST Sun Nov 01 2020 000 WTNT44 KNHC 020252 TCDAT4 Tropical Storm Eta Discussion Number 6 NWS National Hurricane Center Miami FL AL292020 1000 PM EST Sun Nov 01 2020 Eta has continued to become better organized this evening, including the development of an impressive Central Dense Overcast (CDO) with cloud tops colder than -90C near the center, improved banding features in the northwestern semicircle, and the formation of a pinhole mid-level eye noted in 01/2322Z 91GHz SSMI/S microwave imagery. Water vapor imagery also indicates that the upper-level outflow pattern has continued to expand, with dual outflow channels having formed to the northeast and the southwest. Satellite intensity estimates are a consensus T3.5/55 kt from TAFB, SAB, and UW-CIMSS ADT. However, the initial intensity is set a little higher at 60 kt based on the pinhole eye feature...and this intensity estimate is probably conservative. An Air Force Reserve hurricane hunter aircraft is scheduled to investigate Eta in a few hours. Eta has slowed down but is still moving westward, or 270/11 kt. An expansive subtropical ridge that extends from the southwestern Atlantic across the Bahamas, Florida, and into the Gulf of Mexico is expected to keep Eta moving in a general westward direction through Monday morning. By Monday afternoon and evening, the portion of the ridge over the Gulf is forecast to build southward and eastward in the wake of an exiting mid-latitude trough currently moving across the eastern and southeastern United States. The increased ridging will act to force Eta west-southwestward and eventually southwestward over the next 36 hours, resulting in landfall along the northeastern coast of Nicaragua. After moving inland, steering currents are forecast to weaken significantly on days 3-5 as another trough digs southeastward out of the U.S. Plains and into the Gulf of Mexico, eroding the Gulf ridge and causing Eta to drift slowly westward across Central America. Compared to the preponderance of the the model guidance, the HWRF solution of Eta remaining just offshore over the northwestern Caribbean Sea is considered to be an outlier. The new NHC track forecast is very similar to the previous advisory track, and lies close to the simple-consensus models TVCA and GFEX, which are a little to the right of the corrected-consensus model, HCCA. Based on the new NHC track forecast, no changes are required to the existing tropical cyclone warnings and watches in effect. Eta has rapidly intensified 20 kt during the past 12 h. Given the much improved inner-core structure as noted in the SSMI/S imagery, combined with sea-surface temperatures in excess of 29 deg C, mid-level humidity values greater than 80 percent, and the already impressive outflow pattern, Eta should continue to rapidly strengthen until landfall occurs. The main question is: how much strengthening will take place? Some of the more reliable intensity guidance brings the cyclone up to 105-110 kt in 36 hours, with the HWRF model bringing Eta to near category-4 strength. The new NHC intensity forecast shows Eta as a major hurricane in 36 hours when it is expected to be located just inland over northeastern Nicaragua, but a stronger intensity is highly probable just before landfall occurs. Rapid weakening is forecast thereafter while the cyclone moves over the rugged, mountainous terrain of Nicaragua and Honduras, with Eta possibly devolving into a large, quasi-stationary Central American Gyre (CAG). Key Messages: 1. Eta is forecast to strengthen into a hurricane by early Monday morning. Additional strengthening is forecast thereafter, and Eta is expected to be a major hurricane before it reaches the northeastern coast of Nicaragua Monday night or early Tuesday, where a Hurricane Warning is in effect. A Tropical Storm Warning is in effect for a portion of the northeastern coast of Honduras. 2. Through Friday evening, heavy rainfall from Eta will lead to catastrophic, life-threatening flash flooding and river flooding across portions of Central America, along with landslides in areas of higher terrain. Flash and river flooding is also possible across Jamaica, southeast Mexico, El Salvador, southern Haiti, and the Cayman Islands. 3. A life-threatening storm surge, along with damaging waves, is expected along portions of the northeastern coast of Nicaragua near and to the north of where the center makes landfall. Water levels could reach as high as 10 to 15 feet above normal tide levels in some parts of the hurricane warning area. Preparations to protect life and property should be rushed to completion. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 14.9N 80.0W 60 KT 70 MPH 12H 02/1200Z 14.8N 81.3W 75 KT 85 MPH 24H 03/0000Z 14.5N 82.6W 90 KT 105 MPH 36H 03/1200Z 14.1N 83.4W 100 KT 115 MPH...INLAND 48H 04/0000Z 14.0N 84.2W 60 KT 70 MPH...INLAND 60H 04/1200Z 14.0N 85.3W 45 KT 50 MPH...INLAND 72H 05/0000Z 14.2N 86.5W 30 KT 35 MPH...INLAND 96H 06/0000Z 14.9N 88.4W 25 KT 30 MPH...INLAND 120H 07/0000Z 15.7N 88.5W 25 KT 30 MPH...INLAND $$ Forecaster Stewart
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