Weather Blog: August 21, 2025 9 AM (Tropics)

HURRICANE ERIN WILL PASS WELL OFFSHORE OF SOUTHERN NEW ENGLAND BUT STILL BRING HIGH SURF, DANGEROUS RIP CURRENTS, EROSION, AND TROPICAL STORM FORCE GUSTS TO SOUTHERN NEW ENGLAND SHORELINES

Erin Update as of Thursday Morning August 21

Hurricane Erin is off the North Carolina coastline this morning and has just begun to come under the influence of that zonal mid latitude west to east flow.  Erin has turned to the north-northeast and will continue to curve to an east-northeast heading and begin to accelerate in speed.  Erin will pass several hundred miles to the southeast of New England early Friday morning as it accelerates into the North Atlantic.  Erin has begun to show signs of increasing shear and will gradually weaken over the next 24 to 36 hours before losing tropical characteristics.  It will continue, however, to remain a strong post tropical storm with a large radius of storm and gale force winds as it traverses the North Atlantic.

As noted in prior blogs, the large size of Erin and the pressure gradient between Erin and high pressure to the north and west of New England will result in northeast winds with tropical storm force wind gusts over the Cape and Islands and sustained tropical storm force winds not far offshore of Nantucket and the outer Cape this evening into Friday morning.  The rest of the southern New England shoreline will experience brisk northeast winds this evening into Friday.  Over interior southern New England, it will become breezy but not much more than that.

Impacts and Recommended Actions Regarding Erin

High surf and dangerous rip currents have begun to affect the southern New England coastline, especially along the Rhode Island exposed south coast, and the Cape and Islands.  As of 730 AM, 12-foot swells were already encroaching on the New England south coastal waters.  High surf and dangerous rip currents will be an issue through Friday before gradually diminishing.  The high surf and dangerous rip currents will especially impact such locations as the RI exposed south coast beaches, Horseneck Beach in southern MA, Martha’s Vineyard’s South Beach and other exposed south-facing beaches, exposed south and east facing beaches on Nantucket, and the beaches along the ocean side of Cape Cod.  Significant beach erosion may occur during high tides over the next 24 to 36 hours – especially during this evening’s high tide.  An onshore wind in addition to the swells may also increase the risk of high surf and dangerous rip currents for some east and southeast facing beaches north of Cape Cod (all the way to downeast Maine) tonight through Friday.  The National Weather Service has a High Surf Advisory in effect for the RI, MA, NH, and Maine coastlines.

This evening’s high tide (10:43 PM in Boston but earlier in the evening along the RI south coast) in particular may be vulnerable to significant erosion and pockets of coastal flooding from wave overwash along exposed south and southeast facing shorelines.  Due to an increasing northeast wind, even east and northeast facing shorelines along the Massachusetts east coast may experience some splashover and isolated pockets of minor coastal flooding.

A significant maritime impact is expected.  Large swells are expected up to 15 feet along and near shore waters exposed to the open ocean and even higher to 20 feet a short distance offshore late today through Friday morning.  In addition, wind generated waves from northeast winds with tropical storm force gusts (due to the pressure gradient between the hurricane and high pressure to the northwest) will cause extremely treacherous conditions for small craft across most New England coastal waters.  In particular, the combination of a rather strong northeast wind and high southerly swells will also result in a chaotic sea with steep wave profiles over the waters south and southeast of New England.  Owners of small boats may also wish to check moorings in Cape and Island anchorages before tropical storm force gusts arrive late today or early this evening.

Further Information

The National Weather Service monitors the weather 24/7 and updates forecasts, watches, and warnings as necessary.  For most of southern New England, refer to your local Weather Forecast Office for the latest forecast/warning information at weather.gov/box.  For information from other Weather Forecast Offices, go to weather.gov and click on the location of interest on the map.  For the latest information on Atlantic basin hurricane activity, access the National Hurricane Center website at nhc.noaa.gov.

This will be the last blog on Erin.  As always and especially if a mariner, check the latest forecast information from the National Weather Service or your private weather source before undertaking a venture that might increase your vulnerability to the elements.

The motivation to start a blog on Erin was primarily to use this storm as a reminder to prepare or review plans of action in the event of a serious hurricane threat.  We are now heading into the peak of the hurricane season and will likely be monitoring future hurricanes over the next month or two.  Another blog will be issued on any new system that should pose a serious threat to any U.S. coastal area.

About this Blog and Disclaimer

These weather messages are issued when there is a potential risk of hazardous weather to southern New England and serve to provide background information regarding the significant weather with somewhat of an educational slant.  In the case of hurricanes, the author will attempt to issue a message when any portion of the United States coastline may be seriously impacted.  It’s intended to complement and not serve as an alternative to official forecasts issued by the National Weather Service.  Readers are urged to check National Weather Service forecasts and warnings for the most timely and updated weather information.  This weather message is solely produced by the listed author and does not constitute an official product of the Blue Hill Observatory and Science Center (BHOSC).

The frequency of this blog will depend upon the nature of the weather threat and availability of the author.  Thus, for the latest information on weather forecasts and warnings, refer to the National Weather Service, which monitors and forecasts the weather 24/7.

Blue Hill Observatory and Science Center (BHOSC)

The BHOSC maintains a continuous daily observation record that dates from February 1, 1885 without interruption and provides educational information on weather and climate to area students and the community at large.  Your support of BHOSC is much appreciated and enables this nonprofit organization to maintain the long-term climate record at the Blue Hill Observatory (longest continuous record in North America) and provide valuable educational resources on weather and climate via outreach to schools, site visits/tours, webinars, and conferences.  For more information on the Blue Hill Observatory and Science Center, explore bluehill.org.

Next Blog

This will be the final blog on Erin.  Monitor the latest National Weather Service forecasts for specifics as Erin makes its closest approach late tonight or early Friday morning.  Since we are just now entering the peak of the hurricane season, there will likely be future storms to monitor in the coming weeks.

Message issued by:
Bob Thompson
Retired National Weather Service Meteorologist
Blue Hill Observatory and Science Center Board member