Monthly Archives: September 2018

NYC Weather Update – Sept 26, 2018

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Severe thunderstorms could impact the area later today ahead of an approaching cold front. Following the passage of this cold front, conditions will begin to improve, setting us up for a weekend with pleasant, cooler, classic autumn weather.

Rest of today – Storm Prediction Center in Norman, OK has placed parts of the NYC Tri-State (the city, north and west) under a slight risk of severe weather today. Warm, moist air (read: unstable, theta-e rich) is in place with the area in the warm sector of an advancing low pressure center located in Ontario/Quebec. Some rain/thunderstorm activity could take place along a weak warm front this morning. The main focus of activity will occur later today with a cold front approaching from the west.

This cold front will be accompanied by a streak of strong upper level winds (40-50 knots), which will be capable of providing the magnitude of vertical wind shear necessary for some strong to severe thunderstorms to organize. Given the direction of the winds at upper levels being largely parallel to the advancing frontal boundary, expect that the primary storm format will be a QLCS (quasi-lineary convective system) – a line or broken line of storms. High Resolution Rapid Refresh models depict the bulk of storm activity approaching the city around 8PM this evening. Given this storm format and synoptic set up, the most likely severe threat will be damaging wind gusts. Heavy rain could trigger flash flooding as well, since the ground is still quite saturated from yesterday’s rain.

The biggest limiting factor to storm strength today will be overcast skies limiting daytime destabilization from solar heating. As is often the case, I would expect the storms to be weakening somewhat as they approach a more stable marine air layer near NYC. Overall, expect a cloudy day with high temperatures in the low-80s and a muggy feel.

Storm Prediction Center Day 1 Convective Outlook
Weather Prediction Center forecast surface conditions at 8PM EDT
High Resolution Rapid Refresh simulated 1-km radar for 8PM EDT
NAM forecast for 500 mb winds and height valid 8PM EDT

Thursday – the cold front that brings us this possibly severe today will slow down as it pushes south of us, such that it remains close enough that a weak disturbance moving along it could bring us some additional showers late in the day. Skies will be partly sunny with much cooler high temperatures in the upper-60s.

Friday – easterly onshore flow on the back side of this cold front forecast to be to our south will keep skies cloudy with high temperatures around 70°F – chance for showers lingers.

Saturday – high pressure finally starts to take control of sensible weather and should produce a mostly sunny day with crisp conditions and high temperatures in the low-70s.

WxChallenge for Portland International Airport (KPDX) | Sept 25-28

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Temporary Changes to this Blog

Over the next few weeks, I’m going to take a break from my normal posts about weather in NYC and the region because I’m participating in the WxChallenge national weather forecasting competition. This is a course requirement for the final semester of the Undergraduate Certificate in Weather Forecasting program with Penn State University’s World Campus that I’m enrolled in. During the course of this competition, I will be providing forecasts of high temperatures, low temperatures, maximum sustained winds, and total precipitation for various cities in the challenge. The first of these cities will be Portland, Oregon – specifically Portland International Airport (KPDX). If events of particular interest, such as severe weather, tropical storms, or etc are forecast to occur in NYC, I will make special posts regarding such events.

Forecasting for KPDX September 25-28, 2018

Synoptic Set Up (The Big Picture)

High pressure was located at the surface west of KPDX. A rex blocking pattern existed over the Pacific (a upper level high directly north of an upper level low, see animation below, the upper level high is west of OR/WA and shaded with some light blues, the upper level low just south of it shaded with oranges/reds). Some northeasterly winds were forecast during the forecast days, especially later in the day/overnight, which given the topography surrounding KPDX would lead to some downsloping. Still, northwesterly was forecast to be the predominant wind direction, which aligns well with climatological norms for September. A thermal low was mentioned to be in place through the mid-week period that would migrate daily from west to east.

Forecast Rationale

The synoptic set up favors little change in day-to-day conditions. Downsloping and the presence of a thermal low over the Willamette Valley suggest warmer than climatological and MOS (Model Output Statistics) guidance max temps. Despite mostly clear to clear skies throughout the forecast period, radiational cooling at night should be limited due to winds expected to be easterly overnight. When there are clear skies with no/calm winds, this allows infrared radiation to efficiently escape into space from the Earth’s surface, resulting in cooler temperatures when compared with a cloudy and/or windy night. Of note, easterly winds produce the fastest winds for KPDX due to some funneling effects from the Columbia River Gorge (think of this like blowing through a straw). This was referenced in the local forecast AFD. However, the MOS guidance didn’t really show a clear signal of wind directions favorable to strong funneling, so it would be unwise to go too much above guidance here. Late week cool down noted as the rex block breaks down and the upper low that was associated with makes its way towards the west coast. Exact placement/timing could bring some precipitation in the picture by the weekend and maybe early into week 2 forecast period.

Forecast Submitted

Forecast Day Max Temp (°F) Min Temp (°F) Max Sustained Wind

(knots)

 Precipitation (inches)
09/25/2018 82 52 15 0.00
09/26/2018 82 52 11 0.00
09/27/2018 85 54 8 0.00
09/28/2018 83 55 6 0.00

NYC Weekend Weather – Sept 21, 2018

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Cooler weather arrives just in time for the astronomical start of autumn. Cloudy conditions have been persistent, and will continue today. A chance for rain and scattered thunderstorms tonight going into Saturday from a passing cold front. These will not be drenching rains like with the remnants of Florence. High pressure returns Saturday, and should give us a dry weekend, though we may continue to see more clouds than sun.

Rest of today – cool, and cloudy, with high temperatures in the low-70s. Chance for showers and thunderstorms overnight with a passing cold front.

Saturday – sunnier with high temperatures in the mid-70s. The autumnal equinox will take place at 9:54PM EDT.

Sunday – partly sunny with high temperatures in the low-70s.

Monday (Mid-Autumn Festival) – partly sunny with high temperatures again in the low-70s.

NYC Weather Update – Sept 17, 2018

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We had some great late-summer weather this past weekend with high temperatures in the low-80s and lots of sun. Most of this week will be quite nice as well, with the notable exception of Tuesday, when remnants of Florence impact the region and bring around a day of heavy rain. Fortunately, this wet weather will be short-lived, and the remainder of the week should see a return to mostly sunny conditions.

Rest of today – increasing clouds and humidity as remnants of Florence approach from the south. High temperature around 80°F.

Tuesday – periods of rain, heavy at time, with scattered thunderstorms possible. Otherwise cloudy, with high temperatures around 80°F again.

Wednesday – conditions improve as the remnants of Florence quicly move off to the east. A return to mostly sunny weather with cooler highs in the upper-70s as the back side of the cyclonic rotation of the remnants of Florence brings a cold front through.

Thursday – another mostly sunny day with high temperatures in the low-70s, high pressure building should continue to keep things dry for the region.

NYC Weekend Weather – Sept 14, 2018

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After a week of gloomy, cloudy, and at times rainy weather, we will get a nice break this weekend as conditions improve. The same high pressure that’s caused Hurricane Florence to make landfall on the Carolinas by blocking its northward progress will bring us sunnier weather. Indeed, some of the cloud cover over our area is actually a result of outflow from Florence. Its remnants will impact us with rain at some point early next week.

Rest of today – mostly cloudy with high temperatures in the mid-70s as winds continue from the east. High surf with waves 8-12 feet are possible at the coast due to Florence.

Saturday – decreasing clouds as high pressure continues to build. High temperatures around 80ºF.

Sunday – sunny, high near 80ºF, high pressure remains in control.

Monday – clouds and the chance for rain returns. More moist air returns as the high pressure that gives us nice weather over the weekend slides east (and the flow on its western side starts to bring moisture from the south up). We’ll need to monitor the progress of the remnants of Florence as they are likely to bring us rain.

 

NYC Weather + Special Tropical Update – Sept 10, 2018

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This week kicks off with a prolonged period of unsettled weather as a warm front and a cold front both impact the area. Chances for rain will be with us through Wednesday. Conditions finally improve late in the week. We luckily will avoid direct impacts (aside from high surf) from what will be an extremely dangerous Hurricane Florence, which looks set to make landfall on North Carolina late this week. Aside from Florence, two other storms pose threats to US territories this week.

Rest of today – cloudy, with periods of rain, heavy at times, especially later in the day towards the overnight hours. High temperatures will be in the upper-60s with cool, persistent onshore flow from the east. Ahead of an approaching warm front.

Tuesday – chances for thunderstorms will persist into Tuesday, with this slow-moving warm front finally pushing through. There could be thunderstorms overnight. Then, later in the day, as the trailing cold front moves through. Once the warm front passes over, we’ll be within the warm sector of the parent low pressure system, which will allow temperatures to climb into the low-80s with a marked increase in humidity.

Wednesday – the cold front mentioned above will slow down as it approaches us and dissipate. This will lead to continuing chances for rain, and thunderstorms with temperatures again in the low-80s.

Thursday – high pressure will finally begin to build in to our north by Thursday behind the cold front above. This will lead to better conditions, with partly sunny skies and temperatures in the low-80s.

Friday – partly sunny skies with high temperatures in the low-80s again with high pressure to our north.

Florence, Isaac, and Olivia All Pose a Threat to the US

These three storms have the potential to impact the Southeastern US, Puerto Rico, and Hawaii respectively within the next week. Among these, Florence is by far the most dangerous, as it could make landfall on North Carolina as a Category 4 storm with maximum sustained winds of 145 mph.

Hurricane Florence

Over the past day or so, the picture for Florence has become much clearer. Various forecast models have come into remarkable alignment on both the overall track and intensity of Florence over the next 5 days, which means bad news for the Carolinas. The picture looks grim, with Florence set to make landfall as a very strong Category 4 storm packing sustained winds of 145 mph. Florence has nothing but warm water ahead of it, and there should be minimal impact ot this storm from vertical wind shear. Even if the storm weakens due to eyewall replacement cycles prior to landfall, that would only serve to increase the radius of its damaging winds. No matter how you slice it, Florence is likely to bring deadly storm surge and risk of life-threatening flash flooding and inland flooding. The fact that its forecast track slows to a crawl after landfall makes the flooding risk inland especially serious.

Hurricane Isaac

Isaac is a compact storm, which is leading to some uncertainty regarding both its track and intensity forecast. Small tropical cyclones are subject to wild swings in intensity both ways, which can be unpredictable at times. As of now, Isaac is forecast to cross the Windward Islands of the Lesser Antilles as a Category 1 storm, then continue into the Caribbean where hostile shear conditions should cause it to weaken. It is worth noting, despite the UKMET model being an outlier, that there are some signals that the storm could turn to the northwest later in the period, which could mean a threat to Hispaniola and Puerto Rico.

Hurricane Olivia

This storm continues to track towards Hawaii. Although weakening due to the influence of moderate wind shear, it is still set to hit Hawaii later this week as a strong tropical storm. The primary threat to Hawaii from Olivia will be in the form of heavy rain and flash flooding regardless of whether it makes direct landfall on one of the main islands.

NYC Weekend Weather – Sept 7, 2018

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Cooler temperatures are finally upon us after a very hot and humid week. However, the cooler weather also brings a prolonged period of cloudy conditions, with chances for showers each day this weekend. Rain chances continue into the beginning of next week with a storm system approaching. Long-term, we look towards the tropics, as Tropical Storm Florence continues to have the potential for bringing some impacts to the area.

Rest of today – overcast, with much cooler high temperatures in the mid-70s. Chances for showers, especially later in the day.

Saturday – cloudy with high temperatures remain cool in the low-mid 70s with northeasterly onshore flow behind a cold front draped west-east south of us. This front (which passed through yesterday) will become stationary. Multiple impulses of energy will run along this boundary and allow for continued slight chances of showers.

Sunday – yet another cool, cloudy day with chances for rain. High temperatures around 70°F.

Monday – the stationary front stalled out south of us will return north as a warm front. As this happens, chances for rain increase, along with temperatures rising back into the mid-upper 70s.

Will Tropical Storm Florence Impact the East Coast?

Tropical Storm Florence has been active over the eastern and central North Atlantic for over a week now. Within the last few days, Florence underwent a rapid intensification that brought it up to Category 3 status, making it the first major hurricane of the 2018 Atlantic hurricane season. Subsequently, it has weakened to a tropical storm under relentless strong shear. However, it is expected to reintensify into a major hurricane once shear subsides. Worrying trends in the track forecast for Florence continue to allow for the possibility of landfall on the East Coast, or at the very least, substantial coastal impacts like dangerous surf and beach erosion. However, the National Hurricane Center continues to note that there is considerable uncertainty to the track forecast for Florence, such that it is still too early to determine what effects it will have on the East Coast. This storm will warrant careful observation over the coming days and I will have subsequent updates on it.

NYC Weather Update – Sep 4, 2018

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A brief break in the heat over the weekend has led back into another warm spell to begin this week. This latest blast of heat will be short-lived as a backdoor cold front sweeps through tomorrow, followed by another, stronger cold front later this week. Temperatures for the upcoming weekend will once again be comfortable, seasonable to below average. In the tropics, things are starting to get busy with tropical storms Florence and Gordon active and another tropical wave poised to become a tropical cyclone off the coast of Africa. Gordon will make landfall overnight on the Gulf Coast east of New Orleans.

Rest of today – hot and humid with temperatures in the low-90s, mostly sunny skies.

Wednesday – cooler, though still warm with high temperatures in the upper-80s and partly sunny skies. A backdoor cold front will bring cooling onshore southeasterly breezes that help keep a lid on temperatures.

Thursday – temperatures rise back a couple degrees into the low-90s ahead of an approaching cold front from the northwest. The warm air ahead of the cold front could help set the stage for a few scattered strong thunderstorms as the front passes through.

Friday – temperatures cool off quite a bit into the low-80s under mostly cloudy skies. Chance of showers during the day with the cold front lingering south of the area.

Tropics Heating Up

We have 2 active tropical cyclones (Florence, Gordon), and another incipient one in the Atlantic Basin. Tropical Storm Gordon could strengthen into a hurricane before landfall on the Gulf Coast between Mississippi/Alabama overnight into Wednesday. Heavy rain could induce flash flooding in southern portions of these states. The immediate coastline will be at risk of storm surge flooding. Florence doesn’t pose an threat to land. The disturbance shown below that’s furthest east is a tropical wave that’s just emerged off the coast of Africa. This is worth watching as it has a high chance of becoming a tropical cyclone and its eventual track could pose a threat to portions of the Lesser Antilles.