1. Large swells generated by Sam are affecting the Leeward Islands and will spread to portions of the Virgin Islands, Puerto Rico, Hispaniola, the Bahamas, and Bermuda by Thursday or Friday. Significant swells will likely reach the east coast of the United States and Atlantic Canada by the weekend. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials through the upcoming weekend.

There are no coastal watches or warnings in effect.

Key messages for Sam can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT3 and WMO header WTNT43 KNHC.

SURF: Swells generated by Sam will impact the Lesser Antilles for the next several days. Swells are expected to reach Bermuda and the Bahamas mid to late week, and then spread to the United States east coast late this week. These swells could cause life threatening surf and rip current conditions. Please consult products from your local weather office.

At 1100 PM AST (0300 UTC), the center of Hurricane Sam was located near latitude 16.8 North, longitude 53.2 West. Sam is moving toward the northwest near 9 mph (15 km/h), and this motion is expected to continue for the next few days, with an increase in forward speed beginning on Thursday. A turn to the north is expected by Friday. On the forecast track, Sam will pass well to the northeast of the northern Leeward Islands Wednesday and Thursday. Data from a NOAA Hurricane Hunter plane indicate that maximum sustained winds remain near 120 mph (195 km/h) with higher gusts. Sam is a category 3 hurricane on the Saffir Simpson Hurricane Wind Scale. The hurricane could strengthen some overnight, and Sam is anticipated to be a category 3 or 4 hurricane for the next several days. Hurricane force winds extend outward up to 40 miles (65 km) from the center and tropical storm force winds extend outward up to 125 miles (205 km). The estimated minimum central pressure from NOAA aircraft data is 956 mb (28.23 inches).

The NOAA Hurricane Hunters have been flying through Sam tonight, with radar and wind observations showing broken concentric eyewalls at times. The maximum 700-mb flight-level winds on the mission were 114 kt, with peak SFMR values to 103 kt and a central pressure around 956 mb, so the initial wind speed will remain 105 kt. While the overall intensity doesn't seem to have changed much in the past several hours, the aircraft data show that the hurricane has grown in size, and that is reflected in the initial wind radii.

The future intensity of Sam is hard to pinpoint. Eyewall cycles will likely play a key role in determining its second peak intensity since the hurricane should remain in low- or moderate-shear and warm-water environments for the next few days. Those cycles are basically impossible to forecast, but there is some suggestion on satellite that a larger eye is trying to form, which could allow for some increase in strength in the near term. It seems likely that Sam will be a category 3 or 4 hurricane given the conducive environment for most of the forecast period, so the new NHC forecast is similar to the previous one, with the most significant change showing a larger hurricane consistent with the latest guidance.

Sam continues to move northwestward, or 315/8 kt. The hurricane should move in that direction for the next few days around the southwestern portion of the subtropical high. A turn to the north is likely as Sam meets the western edge of the high, with a gradual acceleration to the northeast anticipated by the weekend due to an incoming mid-latitude trough from the west. While there are some speed differences in the models, especially near and after recurvature, the NHC forecast leans toward the faster GFS solution over the slower ECMWF, given the magnitude of the strong southwesterly flow that Sam should encounter at long range, plus a nod to the superior performance of late for the American model. The new forecast is adjusted a bit to the right and faster beyond day 3, with no significant changes made before that time.