Dry weather streak to continue with
warm temperatures thru the weekend Get The Forecast!

*Indications of above or below average temperatures in the table above are relative to what is considered “normal” using data collected over the long term for a particular date. This is collected and maintained by the National Climatic Data Center in conjunction with the National Weather Service actual data from previous years collected at official ASOS/climatology stations across our coverage area. Also note that as time moves forward into a different period as shown above, average temperatures for those dates will also change. See the example below using Philadelphia, PA as the climo station:

The departure from normal uses the average temperature for the date, averaging temps over 24 hours for any given location, using both high and low temperatures hourly during any particular day. This outlook determines warm vs. cool periods relative to normal temperatures.

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Precipitation:

OVERVIEW: September in most areas are seeing near to very slightly below average precipitation departures to this point, with notably drier conditions expected for much of the remainder of September. A long stretch of completely dry weather is expected in the week ahead, with the next decent chance for precipitation holding off until the tail end of September. The month of October will see some increase in precipitation during the first full week and again the 3rd week of October. Overall, the month averages near to slightly below average by the end of the month.

The two precipitation chances in the next week to 10 days are both cold front passages. The first is rather weak, and likely only affects northern areas with isolated showers as a system moves across New England. The associated cold front, albeit weak, will be dragged through the area, and areas closest to the best forcing (northern areas) may see an isolated shower or two at best with it. The 2nd chance is more region-wide and a better opportunity for scattered showers and thunderstorms, but that doesn’t come until Tuesday or Wednesday of the week after next. Until then, much of the region sees very dry conditions continue.

The month of September we project near to slightly below average (-0.0″ to -1.0″) precipitation departure for the month as a whole, with the slightly wetter period to begin the month now behind us, and a much drier 2nd half of the month expected. Looking at the month of October using a blend of ensembles, climate models, and seasonal trends suggests a near to slightly below average (-0.0″ to -1.0″) precipitation departure for the month as a whole. For the remainder of September and all of October, the caveat would be any tropical entities that have the ability to skew the projections higher.

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Breakdown of precipitation departures from normal over the next several weeks:

September 19th – September 25th:  Below average

September 26th – October 2nd:  Near to slightly below average

October 3rd – October 9th:  Near average

October 10th – October 16th:  Near to slightly below average

October 17th – October 23rd:  Near average

Public/free available maps will be updated when a threat is imminent for significant weather on the weather alerts page throughout the year:  //epawaweather.com/weather-alerts/

Note:  Any image in the outlook is clickable for larger viewing

A weak and fast-moving system will move across New England next Friday, and a weak cold front will be dragged through the region. A few isolated showers will be possible mainly in northern areas as the system passes by.

A cold front makes its way through the following Tuesday-Wednesday, and could be accompanied by scattered showers/t-storms. Uncertain at this time is the extent of precipitation along the front given the extended range.

Pattern:

The Madden-Julian Oscillation (MJO): The Madden-Julian Oscillation is currently in phase 4 in the Maritime Continent, which is a La Niña phase, and will remain there at least through early next week. Convection in the Maritime Continent in early Autumn supports troughiness/cooler temperatures, and partly why we will see cooler weather through that period. Most guidance collapses this signal into the Circle of Death (COD) after that point, but remaining close to phases 5/6 in the process. During the past few weeks Atlantic hurricane activity spiked, with wave after wave coming off of the western African coast, and the Caribbean/Gulf of Mexico becoming more active. Currently there are two active storms, Major Hurricane Teddy and Tropical Depression 22, but more areas of interest (invests) are looming coming off of the African west coast. The most notable of these waves is currently a few hundred miles SW of the Cabo Verde Islands. In the nearer term, Tropical Depression 22 is expected to develop into a tropical storm, then hurricane as it meanders in the NW Gulf of Mexico. Hurricane Teddy will likely remain away from our region, but will have to be watched for Maine and Nova Scotia midweek next week.

Average highs and lows continue to drop off during the month of September, but normal high temperatures still remain relatively warm in the 70s. The last 90°F+ temperatures have passed, and won’t be seen again until next Spring/Summer. The last 80°F+ days are close – and in some interior/northern areas, that ship has sailed too. We expect a pattern that will yield a taste of Autumn this weekend and early next week as a trough settles in for that period, then rebounding mid to late week to slightly above average levels. There will be alternating periods of slightly above average and near or near to slightly above average through the end of September, and the month as a whole we think settles at +0.0°F to +2.0°F by month’s end. October likely remains at least slightly warmer relative to average, with the warmest periods found in the 2nd and 3rd weeks of the month. It is important to note that with time, average highs and lows are steadily dropping, and “warmer” periods will be relative to the time of year we are talking about. Use the average highs/lows chart above that provides a point of reference for what average is for each corresponding date, with the examples used for the Philadelphia region.

Tropics: Our attention will be focused primarily on waves coming off of the Western Coast of Africa, but also in the NW Gulf of Mexico in the coming week. Operational guidance and ensembles continue to suggest that while the Atlantic, Caribbean, and Gulf of Mexico remains active through the end of the month, no threats to local interests are expected. For those traveling to northern New England and the Canadian Maritimes, please follow the National Hurricane Center for track updates with regard to Hurricane Teddy. For those traveling to the NW Gulf States, including eastern Texas and coastal Louisiana, what will likely become Tropical Storm Vicky later today will have to be watched closely next weekend.

For the month of September, we expect near to slightly above average temperatures (+0.0°F to +2.0°F) when the dust settles September 30th with high confidence. For the remainder of the month, alternating periods of slightly above average and near or near to slightly below average will occur. Early look at the month of October suggests a slightly above average month (+2.0° to +4.0°F) using longer range climate ensembles and global observation trends. October likely starts off and ends near average, but warmer in the middle two weeks of the month. Lower confidence is listed in the 2nd half of October given the uncertain range of nearly 5-6 weeks from now, and the tendency for climate models to struggle somewhat in the midst of seasonal transition.

Note:  Any image in the outlook is clickable for larger viewing

Plenty of Atlantic activity noted by the National Hurricane Center currently, with two named storms and 4 invests. Attention will be focused on waves coming off of Africa and Hurricane Teddy, but NW Gulf will also be monitored.

An early taste of cooler Autumn temps are expected through early next week, then it briefly warms to toward the end of next week as that trough lifts out. Remaining on either side of average afterwards thru end of September.

Images below are clickable for better viewing

Days 1-5 – confidence VERY HIGH

Days 6-10 – confidence HIGH

Days 11-15 – confidence MODERATELY HIGH

Days 16-20 – confidence MODERATE

Below is a look at the latest Soil Moisture Anomaly for the Contiguous United States. This is used by NOAA/CPC for the purpose of drought monitoring and drought outlooks.

This image will automatically update daily.

Forecaster: EPAWA Meteorologist Bobby Martrich
Discussion last updated: Friday September 18th, 10:30 AM