Mesoscale Discussion
Valid: Mon 16 Oct 2017 02:00 to Mon 16 Oct 2017 07:00 UTC
Issued: Sun 15 Oct 2017 18:43
Forecaster: TUSCHY

A mesoscale discussion was issued for parts of the NE-Atlantic Ocean mainly for extreme wind gusts.

This off-topic MD highlights a non-convective but very dangerous setup over offshore areas of the NE-Atlantic Ocean. The cloud pattern of category-1 hurricane "Ophelia" detoriates rapidly but still indicates a better organized core with weakening convective banding (supporting the idea of and ongoing but tilting deep warm-core structure). Extratropical transformation however is imminent and a vigorous post-tropical depression is forecast during the end of the forecast (and onwards).
Latest WV loops (comparison of two WV channels) show a broadening/lowering and rapidly warming tongue of dry low-stratospheric air to the west of "Ophelia", and this surge is about to approach the southern part of the cyclone's center. Combined with favorable upper dynamics (as described in the extended forecast), another deepening phase is anticipated during the MD forecast period.

Overall synoptic conditions for a potential sting jet or major cold-conveyor belt (CCB) jet event seem to be in place, also supported by numerous fine-mesh models and even global models. Near BL flow exceeds 50-65 m/s in numerical guidance just south of the cyclone's center with a speed maximum near/just below 850 hPa. It's speculative to try to forecast the BL thermal stratifiaction in such an environment (and offshore), but given this wind speed magnitude, gusts in excess of 150 km/h are likely with some models indicating gusts in excess of 180 km/h. The core of the strongest winds will be narrow and probably short-lived compared to the MD's validity, but due to subtle model discrepancies (timing and placement of the cyclone, its deepening rate and transformation into a warm seclusion), a rather broad MD was issued. Convection should not play any role for this event. The most extreme winds should weaken during the end of the MD but intense CCB jet winds approach S-Ireland later-on from the S.