textproduct: Boston / Norton

WHAT HAS CHANGED

The offshore coastal storm has been classified as Subtropical Storm Josephine, though expected impacts across southern New England remain largely unchanged. Brief storm-force gusts are possible across the outer southeastern waters today, but confidence remains too low to upgrade Gale Warnings. Small Craft Advisories will likely be needed as Gale Warnings expire from west to east tonight into Friday.

KEY MESSAGES

- Subtropical Storm Josephine brings showers to far southeastern Massachusetts, along with dangerous marine conditions and gusty winds.

- Fairly cool on Friday with a very low chance of an early morning shower over the eastern waters. Otherwise, moderating temperatures and dry conditions are expected for the weekend into early next week.

DISCUSSION

KEY MESSAGE 1...Subtropical Storm Josephine brings showers to far southeastern Massachusetts, along with dangerous marine conditions and gusty winds.

The coastal storm we've been monitoring this week acquired subtropical characteristics Wednesday afternoon and was classified as Subtropical Storm Josephine by the National Hurricane Center (NHC). The storm remains roughly 250 to 300 miles south-southeast of Nantucket over the warm waters of the Gulf Stream. So, what does this mean for southern New England? Simply put, the change in classification does not alter our expected impacts. As discussed last night, our forecast and messaging remain largely unchanged. In fact, the NHC anticipates Josephine will transition to a post- tropical cyclone later today.

Dangerous to life-threatening marine conditions remain the primary concern, particularly across the ocean waters southeast of Nantucket. Gale Warnings remain in effect across the coastal waters. There is potential for a brief period of storm-force gusts of 50 kt or greater across the outer southeastern waters this morning into early afternoon. However, confidence in the coverage and duration of these stronger gusts remains too low to warrant an upgrade to Storm Warnings at this time.

On land, north to northeast wind gusts of 20 to 30 mph are expected across the interior, with 35 to 45 mph along the coastal plain, strongest across Cape Cod and the Islands. Beach erosion also remains possible along east-facing shorelines due to persistent northeast winds and large waves.

As of early this morning, KBOX radar returns show a shield of precipitation pivoting westward toward Cape Cod and the Islands. However, much of this precipitation is struggling to reach the ground due to dry air near the surface associated with high pressure to our north. Most of southern New England will remain dry, although a few light showers could extend as far west as southeastern Massachusetts, generally east of a New Bedford to Plymouth line. The greatest chances for measurable rainfall remain from Nantucket to Chatham through the first half of today.

Farther west, sunshine will allow temperatures to reach the middle 60s, while persistent cloud cover across eastern portions of the region will keep highs in the upper 50s to lower 60s. Northeast winds gradually diminish from west to east this afternoon as Josephine tracks northeast into the North Atlantic, aided by an approaching northern-stream shortwave and associated trough.

KEY MESSAGE 2...Fairly cool on Friday with a very low chance of an early morning shower over the eastern waters. Otherwise, moderating temperatures and dry conditions are expected for the weekend into early next week.

As Josephine transitions to a post-tropical cyclone and departs into the North Atlantic, surface high pressure builds into southern New England from the west. A northerly breeze will likely persist Friday, although winds will be considerably lighter than the past few days as the pressure gradient relaxes. Despite abundant sunshine, northerly flow will maintain a cooler air mass, with highs mainly in the lower to middle 50s. An isolated shower cannot be ruled out over the eastern coastal waters early Friday, but otherwise dry conditions are expected.

Depending on how quickly winds decouple Friday night, Saturday morning could feature a frosty start across portions of the interior, with lows in the upper 20s to middle 30s. Similar overnight temperatures are possible Sunday morning as well.

Otherwise, high pressure promotes subsidence and generally quiet weather through the weekend and into early next week. Temperatures gradually moderate, with daytime highs returning to the lower and middle 60s and overnight lows increasing a few degrees each day as warmer air advects into the region aloft.

Looking ahead to Tuesday, guidance suggests a cold front may approach southern New England. However, the front will be situated between two strong areas of high pressure, limiting available moisture and potentially slowing its southward progression. High pressure may even suppress the front, allowing dry conditions to persist into Wednesday. Uncertainty remains regarding the timing and strength of any frontal passage, so it is still too early to provide much detail on associated sensible weather impacts.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

12Z TAF Update:

Today...High confidence in trends.

VFR conditions prevail at most terminals with the exception of the Cape/Islands terminals this morning with MVFR ceilings. Few remaining showers clip the outer Cape and ACK this AM, but should end by 14/15Z. Ceilings improve to VFR between 16Z and 19Z for Cape/Islands. NE winds of 15 to 25 kt along the eastern and southeastern coast, with gusts of 25 to 40 kt. Strongest gusts expected at ACK, with lower gusts along the coastal plain. Farther inland, N winds of 10 to 14 kt with gusts of 20 to 25 kts.

Tonight...High confidence.

VFR. N to NNW winds gradually diminish in the evening. Some sites may lose gusts for a period before a weak front pushes south 00-03Z which may bring a period of gusts 18-24 kts overnight. Winds stronger along the eastern and southeastern coast, with sustained speeds of 10 to 15 kt and gusts of 20 to 30 kts.

Friday...High confidence.

VFR. Northerly winds across much of the region, though winds remain elevated east/southeast of I-95, with sustained speeds of 8 to 12 kt and gusts of 18 to 25 kts. Winds gradually decrease through the afternoon/evening Friday in those locations.

KBOS Terminal...High confidence in TAF.

VFR. Gusty northerly winds continue today, with sustained speeds of 10 to 14 kt and gusts of 25 to 30 kt. Gusts decrease after 21Z this afternoon, potentially diminishing for a period early this evening. A front moves through 00-03Z bringing another period of gusts 18-25 kts out of the N. Marginal gusts may stick around through the early afternoon Friday before diminishing.

KBDL Terminal...High confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night: VFR. Breezy. Areas frost.

Saturday: VFR.

Saturday Night: VFR. Areas frost.

Sunday through Monday: VFR.

MARINE

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Through Friday...High confidence in hazardous marine conditions, though lower confidence in the potential for storm-force gusts across the outer southeastern waters.

Dangerous to life-threatening marine conditions continue as Subtropical Storm Josephine remains offshore of southern New England. Strong high pressure to the north, combined with Josephine to the southeast, maintains a tight pressure gradient across the coastal waters, resulting in persistent northeast winds and large seas.

Gale Warnings remain in effect across all coastal waters through at least 8 PM this evening, with northeast wind gusts generally ranging from 30 to 45 kt. However, there is potential for a brief period of storm-force gusts of 50 kt or greater across the outer southeastern waters this morning into early afternoon. Given lower confidence in the coverage and duration of these stronger gusts, opted to maintain Gale Warnings rather than upgrade to Storm Warnings. Seas remain rough, potentially reaching 15 to 16 feet across portions of the outer waters.

As Josephine tracks northeast into the North Atlantic, winds gradually diminish from west to east this evening. Gale Warnings across the waters west of Nantucket and Martha's Vineyard are expected to expire at 8 PM, with Small Craft Advisories needed thereafter for lingering gusty winds and elevated seas. Farther east, gale-force gusts will persist longer, with Gale Warnings continuing through early Friday afternoon. Once these warnings expire, Small Craft Advisories will likely be needed as winds gradually subside but seas remain elevated.

Marine conditions continue to improve Friday night and into the weekend as Josephine pulls farther away and high pressure builds into southern New England. However, elevated seas may linger beyond the strongest winds.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Areas of rough seas.

Saturday: Winds less than 25 kt. Local rough seas.

Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.

Sunday Night: Winds less than 25 kt.

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ230. Gale Warning until 2 PM EDT Friday for ANZ231>234-250-251-254- 255-280>282. Gale Warning until 8 PM EDT this evening for ANZ235-237-256- 283. Small Craft Advisory until 8 PM EDT this evening for ANZ236.