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 during the next several days. Swells are expected to reach Bermuda and the Bahamas in a couple of days, 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 500 PM AST (2100 UTC), the eye of Hurricane Sam was located by an Air Force Reserve Unit Hurricane Hunter aircraft near latitude 17.9 North, longitude 55.0 West. Sam is moving toward the northwest near 9 mph (15 km/h), and this general motion with an increase in forward speed is expected during the next couple of days. A turn toward the north is forecast by Friday. On the forecast track, Sam will pass well to the east or northeast of the northern Leeward Islands through Wednesday. Maximum sustained winds are near 130 mph (215 km/h) with higher gusts. Sam is a category 4 hurricane on the Saffir Simpson Hurricane Wind Scale. Some fluctuations in intensity are expected during the next couple of days, but Sam is forecast to remain a major hurricane through late this week. Hurricane force winds extend outward up to 40 miles (65 km) from the center and tropical storm force winds extend outward up to 140 miles (220 km). The minimum central pressure estimated from Air Force Hurricane Hunter aircraft observations is 947 mb (27.97 inches).

Sam has looked a little less impressive on satellite imagery this afternoon, particularly on the infrared channels where the eye is not very well-defined. However, observations from the Air Force Hurricane Hunters indicate that the hurricane is maintaining category 4 intensity since a blend of the latest flight-level and SFMR-observed surface winds support maintaining 115-kt winds. The aircraft also measured a quite low central pressure of 947 mb on two passes through the eye. Upper-level outflow remains well defined except over the southwest quadrant of the circulation, and several arc clouds are seen emanating from the system over the western semicircle, indicative of some dry mid-level air in the environment. However, this dry air is apparently not significantly affecting the inner core of Sam, given that it has remained a powerful hurricane.

Center fixes yield a continued slow northwestward motion of around 305/8 kt. There is little change to the track forecast reasoning from the previous advisories. Sam is likely to move around the southwestern periphery of a subtropical ridge for the next couple of days. A turn toward the north, ahead of a large mid-tropospheric trough moving off the United States east coast, is forecast around day 3. Later in the forecast period, the hurricane is expected to accelerate northeastward within the flow on the eastern side of the trough. There is good agreement among most of the guidance models on this general track, and the official forecast is very close to the model consensus.

Since Sam will remain in a low-shear environment and over a warm ocean surface for the next few days, some re-intensification is possible, and the system is likely to remain a major hurricane for the next 4 days or so. The official intensity forecast is not much different from the latest NOAA corrected consensus forecast, HCCA.