Marine Weather and Tide Forecast for Portland, CT

KEY MESSAGES
1) Warming trend early into midweek. Dry until Wednesday.

2) Rain showers return Wednesday with some thunderstorms possible.
Showers could continue into Thursday with growing concerns for severe thunderstorms.

3) Strong heat returns for Thursday into Friday, with heat indices nearing 100 in some places.

4) A cold frontal passage will likely tamp down temperatures at least a little for this weekend into the beginning of next week.

DISCUSSION

KEY MESSAGE 1
Today was a mild day, but a warming trend will continue into mid- week. High pressure at the surface is located very near the area with riding continuing to build in aloft. This will keep skies clear and allow for decent radiational cooling tonight with lows in the 50s.

Highs Tuesday warm into the 70s for much of the coast with the NYC metro and interior areas N & W of NYC getting into the 80s.
Mostly sunny skies should hold as high pressure remains in control at least through Tuesday night as it moves offshore.

KEY MESSAGE 2
A shortwave aloft will gradually traverse the region on Wednesday and Thursday allowing for low pressure at the surface to impact the region and bring chances for showers and even thunderstorms.

S to SW flow will lead to higher moisture transport into the area with PWATs on both Wednesday and Thursday peaking between 1.5 to 2". For reference the SPC Sounding Climatology shows this is essentially the 90th percentile to just above the max for this time of year. Dewpoints also look to rise into the mid 60s to low 70s.
With a moist air mass in place and a passing shortwave aloft, showers appear to grow in coverage west to east on Wednesday, becoming likely by Wednesday afternoon. This will limit our instability and high temperatures. This should mainly be a shower event, but a few embedded thunderstorms could pop up on Wednesday, especially in areas N & W of NYC.

Thursday appears to have a better potential for thunderstorms, along with a risk for severe weather. The shortwave aloft moves to the east with ridging building in from the west. This allows heights to grow aloft on Thursday. Skies will clear out some with partly cloudy conditions through the morning and early afternoon. However, dewpoints and PWATs will be elevated Thursday afternoon and evening.
This occurs in tandem with very strong heating at the surface.

By Thursday afternoon, we should be primed for thunderstorms to pop up in areas N & W of NYC, then pass eastward across the area into the evening. With strong heating in place and only a weak cap, thunderstorms could get started earlier than anticipated. The GFS is bringing SBCAPE values as high as 2,600 J/kg in areas N & W of NYC with values remaining above 1,000 J/kg as you get east of NYC, then dropping altogether as storms advance east and evening takes over.
Bulk shear is not all that impressive around 15-30 kt, but mid-level lapse rates reach 7.2 C/km on the 12Z GFS and 7.4C/km on the 12Z NAM. Model soundings also show a good amount of turning of the winds with altitude.

Details still remain murky this far out on severe thunderstorm chances on Thursday until the event enters the time window of CAMs, but at this point we're keeping an eye out for growing potential for damaging wind gusts and large hail. One thing that will really work against them from developing is ridging aloft.

Any thunderstorms could bring with them heavier downpours, but they should be moving fast enough to prevent any major concerns for flooding. Our ongoing drought also helps mitigate flash flooding concerns.

KEY MESSAGE 3
A 580-585 dam ridge takes over aloft Thursday into Friday under a moist airmass with SW to S flow keeping dewpoints elevated. This will allow high temperatures to climb into the 90s both days with heat indices in the mid to upper 90s on Thursday. By Friday, western parts of the area into the NYC metro could see heat index values approach or exceed 100.

Rain chances should keep the period of higher heat confined to the late morning and early afternoon on Thursday. Friday will be drier with any rain not anticipated until at least Friday night with a cold front, so heat could persist into the late afternoon.

KEY MESSAGE 4
A cold frontal passage is modeled to occur in the Fri night to early Sat time period. This far out, timing is highly uncertain. However, this timing will be critical, as an overnight passage will likely have far fewer impacts than a Sat aftn passage. If the front slows and does pass Sat aftn, a solid severe event seems likely.

Regardless of timing, the front will serve to cool temps down at least a little over the weekend and into the start of next week.
Again, timing critical with Sat temps, but the model consensus is currently quick enough to trend the numbers down. The current fcst overall may be a bit too high based on the MEX, especially further out where the NBM is about 10 degrees warmer on Mon.

AVIATION /06Z TUESDAY THROUGH SATURDAY/
High pressure to the south gradually shifts further offshore.

VFR.

Light WSW or SW flow into the morning, though could be more variable at outlying terminals at times. SW-S winds increase to 10-15 kt by early afternoon, and could be a little stronger (15-20 kt) at KJFK with ambrose jet development likely enhancing speeds here. Gusts around 20 kt possible at city terminals as well, with an occasional gust possible elsewhere. Any gusts subside in the evening, and SW flow continues into Wed AM, speeds under 10 kt.

...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

Gusts may be more occasional at times.

Sustained speeds at JFK could briefly exceed 20 kt mid to late afternoon.

OUTLOOK FOR 06Z WEDNESDAY THROUGH SATURDAY

Late tonight: VFR.

Wednesday: MVFR or lower possible in showers during the afternoon/evening. Thunderstorms possible, primarily north and west of the NYC metros. SW winds G20kt.

Thursday-Friday: MVFR or lower possible at times w/ chances of showers and thunderstorms in the afternoon and evening.

Saturday: Generally VFR.

Detailed information, including hourly TAF wind component forecasts, can be found at: https:/ www.weather.gov/zny/n90

MARINE
Sub-SCA conditions are expected to continue with high pressure in control through tonight. The high pressure area moving farther southeast into the Western Atlantic will make for more of a southerly flow and fetch on Tuesday. The pressure gradient is expected to tighten and with Ambrose jet likely to develop, western ocean zones west of Moriches Inlet could gust near SCA levels for some time late in the afternoon Tuesday into the early evening Tuesday. Otherwise, sub-SCA conditions are forecast to continue across the other marine zones. Sub-SCA conditions are anticipated Wed-Thu.

Winds and seas are expected to remain blw SCA levels Fri thru the upcoming weekend. There could however be strong tstms with a cold frontal passage in the Fri night thru Sat time period.

Rip Currents...

For today, the rip current risk is moderate as winds gain a more onshore component today near 10 kt with a lingering easterly ocean swell of near 3-4 ft and 5 sec period. Wave heights are expected to be near 3 to 4 ft.

For Tuesday, the rip current risk is also moderate. Southerly winds of near 10 to 15 kts are expected with gusts near 20 kt.
Southerly ocean swells near 3-4 sec and easterly ocean swells near 6-8 sec are expected with the southerly one increasing in the afternoon. Wave heights of near 2 to 3 ft are expected.

OKX WATCHES/WARNINGS/ADVISORIES
CT...None.
NY...None.
NJ...None.
MARINE...None.