T/S 'Erin' Discussion from National Hurricane Center:
Erin is moving quickly off to the west, with the motion estimated at 275/17 kt. Over the next few days, this motion should continue with possibly some slight south-of-due-west motion. Erin's motion is primarily influenced by an east-to-west oriented mid-level ridge draped across the subtropical Atlantic basin. By the end of the forecast period, this ridge may start to become more oriented to the northeast of Erin, inducing a more poleward motion by 120 h.
The initial NHC track forecast elects to stick fairly close to the HFIP corrected consensus approach (HCCA), which is a touch on the south side of the overall track guidance envelope. It should be noted that spread in the track guidance, especially the ensembles, begins to increase markedly at the end of the forecast period. The intensity forecast in the short-term is a little tricky. The earlier scatterometer data indicate the system has a small circulation which could be prone to rapid intensity changes, either up or down. While vertical wind shear over the system is forecast to be low, between 5-10 kt over the next 72 hours, sea-surface temperatures are more marginal, around 26-27C, with a decent amount of dry mid-level air along the path of the tropical storm.
The first NHC intensity forecast will thus only forecast slow intensification in the short-term, assuming the marginal SSTs and lack of mid-level moisture will keep the small vortex in check. After 48 h, however, the SSTs start to gradually increase and should allow the local environment of Erin to moisten up. Thus, the rate of intensification will likely increase in the second half of the forecast period. The NHC intensity forecast is a little on the high side of the guidance in the short-term, partially due to the initial intensity, but is in line with the HCCA intensity aid. By 120 h, the hurricane-regional models (e.g., HWRF/HAFS), and statistical-dynamical aids (EC-SHIPS/LGEM) show Erin becoming a major hurricane, and that will be explicitly forecast at the end of the period.
- Forecaster Papin