Marine Weather and Tide Forecast for Cape St. Claire, MD

KEY MESSAGES
1. Dry conditions expected through much of tonight, however a few isolated showers or storms may arrive by around dawn Wednesday. Warmer today, but with humidity remaining low.

2. Dangerous heat is likely during the latter portion of the week.

3. There are multiple chances for thunderstorms Wednesday through Monday.

DISCUSSION
KEY MESSAGE 1...Dry conditions expected through much of tonight, however a few isolated showers or storms may arrive by around dawn Wednesday. Warmer today, but with humidity remaining low.

Broad upper ridging will build through tonight. At the surface, high pressure will slide offshore, beginning a transition to a warm advection regime which will ramp up late tonight as a warm front lifts north. A mid level shortwave trough associated with upstream convection will approach the area by dawn Wednesday.

Following a cool morning, high temperatures this afternoon will be mainly in the low to mid 80s (mid to upper 70s for the immediate coast and higher elevations). The high pressure departing offshore will be just slow enough to prevent moisture return and keep our dewpoints low today, mixing out into the 40s to low 50s by early afternoon. This will keep conditions very comfortable despite the increasing temperatures. Enjoy it while it lasts though, as we do not have dewpoints this low in the forecast again for at least the next 7 days. Scattered cumulus developing with scattered to broken cirrus today, thickening up later in the day.

Lows tonight will be upward of 10-15 degrees warmer than this morning, mainly in the mid 50s to mid 60s under increasing cloud cover. We'll have to keep an eye on the remnant convection approaching from upstream overnight. Current indications are that instability will weaken considerably toward the east as the remnant activity moves in overnight into our area. This will likely result in some isolated decaying showers and embedded rumbles of thunder moving in around dawn or so across the western half of the forecast area.

KEY MESSAGE 2...Dangerous heat is likely during the latter portion of the week.

In general, mid-level ridging is expected to build into the region during the middle and latter part of the week. However, guidance has been trending southward with placement of an upper- low over Canada and associated troughing over the CONUS, and therefore featuring a slightly weaker ridge axis through our region. In addition, it appears increasingly likely that at least a few shortwave impulses will traverse the region. At the surface, the region will be under the influence of high pressure centered over portions of the Southeast, with a few subtle fronts potentially passing through the area.

Despite these subtle changes, dangerous heat is still expected across the area, with Thursday and Friday currently looking like the hottest days. Temperatures on both days look to climb into the low to mid 90s across most of the area. With dewpoints generally in the low 70s, heat indices are expected to climb into the upper 90s, with low 100s looking increasingly likely across portions of southeastern PA, southern NJ, and the Delmarva. This level of heat and humidity can become dangerous quickly for sensitive individuals and those outdoors for extended periods of time. It still appears likely that heat headlines will eventually be necessary during this time period to cover this threat.

A cold front looks to move through the region late Friday into Saturday, which will likely knock temperatures and dewpoints down. Though it will still be hot, at least some relief appears probable for the weekend and into early next week.

KEY MESSAGE 3...There are multiple chances for thunderstorms Wednesday through Friday.

It still appears that the pattern in place will become increasingly conducive for precipitation chances across the region beginning on Wednesday. Much of this activity looks to be in the form of diurnally driven convection, though some guidance is beginning to indicate a few better opportunities for more widespread shower and storm development.

The first opportunity appears to come on Wednesday, with a weak shortwave and surface trough moving through the region. Given somewhat limited instability and little shear, severe weather potential currently appears low. As of right now, PoPs are around 40- 60% across the Delmarva and southern NJ, and 60-80% for eastern PA and northern NJ. It should be noted that even with the high PoPs, not everywhere will see rain given the scattered nature of the expected convection. Thursday features a less obvious trigger for convection, but isolated to scattered showers and storms are still possible. PoPs are generally 30-60%.

On Friday, the region is expected to begin feeling the influence of the upper trough to the west of the region. In addition, a cold front at the surface will approach the area late Friday into Saturday. Scattered showers and storms may focus near and ahead of this boundary, and with strong destabilization and slightly better wind fields aloft, there is concern that some severe threat could materialize. This will need to be monitored in the coming days.

Guidance continues to trend drier for the first part of the weekend in the wake of the cold front. However, another front may approach towards the end of the weekend and into early next week, so the pattern is expected to remain fairly unsettled.

AVIATION /06Z TUESDAY THROUGH SATURDAY/
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Through 12Z...VFR. Winds less than 5 kts, to locally calm, favoring a SSW direction. High confidence.

Today...VFR. SSW winds increasing to near 10 kts by 16Z. Some occasional gusts up to 20 kt are possible, but have left out of the TAFs for now. SCT clouds around 4-6 kft AGL likely during the afternoon, otherwise, increasing high clouds late. High confidence.

Tonight...VFR to start, and for much of the night. By 09Z or so, a few isolated showers and SCT to BKN MVFR ceilings will develop. Southerly winds near 5-10 kts. High confidence in VFR through 09Z, then low confidence on timing/coverage of any restrictions from stratus or showers.

Outlook...

Wednesday through Wednesday night...Periods of sub-VFR conditions likely in scattered showers and storms.

Thursday through Thursday night...Primarily VFR. Brief periods of sub-VFR conditions can't be ruled out in isolated to scattered afternoon showers and storms.

Friday through Friday night...Periods of sub-VFR conditions are possible in scattered showers and storms.

Saturday...Primarily VFR. An isolated shower or storm is possible.

MARINE
No marine hazards expected through tonight. Southerly winds increasing to 10-15 kts with gusts up to 20 kts and seas 2-3 feet.

Outlook...

Wednesday through Wednesday night...SCA conditions are possible with south winds 15-20 kt and gusts near 25 kt, becoming southwest Wednesday night and diminishing late. Seas 3-5 feet, also diminishing late Wednesday night.

Thursday through Saturday...No marine headlines currently anticipated. Winds under 25 kt and seas under 5 feet.

Rip Currents...

For today, light south winds in the morning will increase to 10 to 15 mph with gusts up to 20 mph in the afternoon. Breaking waves will average 1 to 2 feet with a light easterly swell with a period around 7 seconds. As a result, there is a LOW risk for the development of dangerous and life threatening rip currents at the Jersey Shore and at Delaware Beaches.

On Wednesday, south winds increase to 15 to 20 mph with gusts up to 30 mph. Breaking waves will be 1 to 3 feet with a light easterly swell around 8 seconds. This will result in a LOW risk for the development of dangerous and life threatening rip currents at the Jersey Shore in Monmouth county and Delaware Beaches, and a MODERATE risk at the Jersey Shore in Ocean, Atlantic, and Cape May counties.

Ocean water temperatures are gradually increasing, but remain mostly in the 60s.

For specific beach forecasts, visit weather.gov/beach/phi

PHI WATCHES/WARNINGS/ADVISORIES
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.