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WTNT45 KNHC 210839

TCDAT5

 

Hurricane Nigel Discussion Number  24

NWS National Hurricane Center Miami FL       AL152023

500 AM AST Thu Sep 21 2023

 

Nigel is starting to feel the effects of increased vertical wind

shear this morning. Proxy-vis and infrared satellite imagery show

that the large, ragged eye from the past few days has become

obscured. An AMSR microwave pass at 0513 UTC confirmed that the

eyewall structure has collapsed, and a thick curved band on the

northern side is all that remains.  Vertical wind shear has the deep

convection displaced to the northern side of the system, within the

main banding feature, with cold cloud tops in the northwest

semicircle near -70 Celsius. Subjective satellite current intensity

(CI) values were 4.5 from both TAFB and SAB. Given the degradation

in the satellite appearance and these estimates, the initial

intensity is set to 75 kt for this advisory.

 

Nigel is moving swiftly to the northeast at an estimated motion of

50/ 26 kt. The system is currently moving within the flow ahead of a

mid-latitude trough off the northeast US Coast and Atlantic

Canada, with this quick northeast motion expected to continue

during the next day or two. Late Friday and into the weekend,

models show Nigel interacting with a larger polar low over the

North Atlantic. The NHC track forecast is very similar to the

previous advisory and remains near the consensus aids.

 

The hurricane is moving into a more hostile environment with

vertical deep layer shear forecast to further increase, and sea

surface temperatures along the forecast track continue to cool over

the northern Atlantic. Nigel is also entering a drier mid-level air

mass with relative humidities below 40 percent. Nigel should begin

to transition into an extratropical cyclone very soon, and this

process is expected to be complete in about 24 hours. The ECMWF and

GFS SHIPS guidance show extratropical transition occuring even

sooner than what is forecast. The official intensity forecast shows

gradual weakening, with Nigel becoming a powerful extratropical

cyclone on Friday.  By the end of the forecast period, Nigel will

become absorbed in the aforementioned larger polar low.

 

 

FORECAST POSITIONS AND MAX WINDS

 

INIT  21/0900Z 40.6N  47.8W   75 KT  85 MPH

 12H  21/1800Z 42.9N  42.7W   70 KT  80 MPH

 24H  22/0600Z 45.9N  35.0W   60 KT  70 MPH...POST-TROP/EXTRATROP

 36H  22/1800Z 49.5N  27.5W   50 KT  60 MPH...POST-TROP/EXTRATROP

 48H  23/0600Z 53.1N  23.6W   50 KT  60 MPH...POST-TROP/EXTRATROP

 60H  23/1800Z 56.8N  23.1W   50 KT  60 MPH...POST-TROP/EXTRATROP

 72H  24/0600Z 58.3N  24.4W   45 KT  50 MPH...POST-TROP/EXTRATROP

 96H  25/0600Z...DISSIPATED

 

$$

Forecaster Kelly