Hurricane Sam Remains A Powerful Category 4 Hurricane

What you need to know:
– Sam is forecast to continue moving northeast of the Lesser Antilles, safely northeast of the Leeward Islands, posing no direct threat to T&T and the Lesser Antilles.
– The National Hurricane Center is forecasting Sam to remain at Category 4 strength, with fluctuations in intensity through the next 36 hours.
Swells from Hurricane Sam are forecast to continue affecting the northern and eastern coastlines of the Lesser Antilles through the end of the week.
– Due to near calm winds induced by Sam, very hot temperatures are forecast across the region with localized, slow-moving, possibly severe, afternoon showers and thunderstorms across western and hilly areas.

The Latest From The National Hurricane Center

Hurricane Sam's Forecast Track as of 5:00 PM Tuesday 28th September 2021. (National Hurricane Center)
Hurricane Sam’s Forecast Track as of 5:00 PM Tuesday 28th September 2021. (National Hurricane Center)

At 5:00 PM AST, the center of Hurricane Sam was located by an Air Force Reserve Unit Hurricane Hunter aircraft near latitude 17.9°N, 55.0°W. Sam is moving toward the northwest near 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 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 65 kilometers from the center and tropical-storm-force winds extend outward up to 220 kilometers. The minimum central pressure estimated from Air Force Hurricane Hunter aircraft observations is 947 millibars.

Hurricane Sam's latest information as of 5:00 PM Tuesday 28th September 2021. (National Hurricane Center)
Hurricane Sam’s latest information as of 5:00 PM Tuesday 28th September 2021. (National Hurricane Center)

Hurricane Sam’s Watches & Warnings

Hurricane Sam's Tropical Storm Watches and Warnings as of 5:00 PM Tuesday 28th September 2021. (National Hurricane Center)
Hurricane Sam’s Tropical Storm Watches and Warnings as of 5:00 PM Tuesday 28th September 2021. (National Hurricane Center)

There are no coastal watches or warnings in effect at this time.

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.

Swells have been affecting Trinidad and Tobago’s northern and eastern coastlines, causing choppy seas in nearshore areas.

Hurricane Sam's probabilities for tropical-storm-force winds as of 5:00 PM Tuesday 28th September 2021. (National Hurricane Center)
Hurricane Sam’s probabilities for tropical-storm-force winds as of 5:00 PM Tuesday 28th September 2021. (National Hurricane Center)

This system is of no direct threat to Trinidad and Tobago.

Hurricane Sam’s Forecast Discussion

Hurricane Sam (Weathernerds.org)

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.

Key Messages:

  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.

Tropical Cyclone Climatology

2021 has already produced 19 tropical cyclones in the Atlantic Basin, with the next system being named Victor for the 2021 Atlantic Hurricane Season. For this time of year, most systems form in the Caribbean, the Gulf of Mexico, and off of the Eastern United States.

As we head through the last few days of September and into October, we’ll continue to monitor the entire Atlantic closely as tropical cyclones could form from tropical waves, non-tropical low-pressure systems in the North Atlantic, and from the Central America Gyre in the Western Caribbean Sea or the southwestern Gulf of Mexico.

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