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 day or two, and then spread to the United States east coast by this weekend. These swells could cause life threatening surf and rip current conditions. Please consult products from your local weather office.

At 500 AM AST (0900 UTC), the center of Hurricane Sam was located near latitude 18.9 North, longitude 56.2 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 and northeast of the northern Leeward Islands through tonight. Data from an Air Force Reserve Hurricane Hunter aircraft indicate that the 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 125 miles (205 km). The latest minimum central pressure estimated from reconnaissance aircraft data is 950 mb (28.06 inches).

The eye of Sam has become cloud filled in infrared satellite imagery overnight, but the ring of deep convection surrounding the eye has cooled. There appears to be a southwest-to-northeast tilt to Sam's circulation as some modest southwesterly shear seems to be impinging on the hurricane. An Air Force Reserve Hurricane Hunter aircraft that has been investigating Sam overnight shows that the hurricane continues to fluctuate in intensity. The aircraft has reported a peak flight-level wind of 124 kt and SFMR winds of 108 kt. Therefore the initial wind speed has been set at 115 kt, which leans toward the higher flight-level-to-surface wind reduction. The aircraft also reported a minimum pressure of 950 mb, which is up a few millibars from the flight yesterday afternoon. The fluctuations in intensity that Sam has experienced over the past couple of days are fairly typical for hurricanes of this strength.

As mentioned in the previous advisory, Sam will be moving into a lower vertical wind shear environment, and the expected faster forward speed decreases the potential for upwelling beneath the storm. As a result, some re-intensification is forecast, but difficult-to-predict eyewall replacement cycles could cause additional fluctuations in intensity over the next day or two. After 60 to 72 hours, a more pronounced weakening trend is likely to begin as the storm moves over cooler SSTs and the vertical shear increases. The global models indicate that Sam will begin its transition into a powerful extratropical cyclone late in the period, but that transition will likely not be completed until after 120 h.

Sam is moving northwestward at about 8 kt. The track guidance remains in excellent agreement through 96 hours as Sam should move northwestward and then northward around the western portion of the subtropical ridge over the eastern Atlantic during the next few days. By Saturday, Sam is forecast to turn northeastward between the aforementioned ridge and a deep-layer trough over the northeastern U.S. and Nova Scotia. By late in the period, there is an increase in spread in the guidance which is related to how Sam interacts with the deep-layer trough. For now, the NHC track forecast at days 4 and 5 lies between the TVCA multi-model consensus and the HFIP corrected consensus aid. Overall, little change to the previous NHC track forecast was required for this advisory.

Sam has a well-organized cloud pattern on satellite imagery, with a 90 n mi-wide Central Dense Overcast surrounded by numerous convective banding features. Upper-level outflow has now become better established to the southeast of the hurricane. A NOAA Hurricane Hunter mission from a couple of hours ago reported a 20 n mi-wide diameter circular eye. The current intensity is held at 115 kt for this advisory, which is a little higher than the maximum winds observed in the earlier aircraft mission. However, since the estimated minimum central pressure of 949 is a little lower than it was earlier this morning and Sam's intensity has been fluctuating, it is considered prudent not to lower the winds at this time. An Air Force Hurricane Hunter aircraft is scheduled to investigate the hurricane soon and will provide another intensity estimate.

Sam continues its slow northwestward trek with the current motion remaining near 310/8 kt. Sam should move northwestward and then northward around the western portion of the subtropical ridge over the eastern Atlantic during the next few days, and turn toward the north-northeast and northeast later in the forecast period. The track guidance models are in very good agreement through 72 hours or so, with some increase in model spread thereafter. This increase in spread is largely due to how Sam will interact with a strong mid-latitude trough moving through Atlantic Canada. Some of the guidance suggests that this trough could partially bypass the hurricane around the end of the period and beyond, but this is not yet clear. The current NHC forecast track is not much different from the previous one and is in good agreement with the dynamical model consensus, TVCA.

The hurricane will continue to move over warm waters and in an environment of low vertical shear and diffluent upper-level flow for the next 1-2 days. Thus, it would not be surprising to soon see some restrengthening. The official intensity forecast is essentially a blend of the latest Decay-SHIPS and LGEM predictions, and is very similar to the previous NHC forecast. Sam is likely to remain a major hurricane into this weekend.