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Unsettled and Cooler Conditions Dive In, Irma Becomes a Category 4 Hurricane

Good Evening and Happy Labor Day! 

Today was a rather big improvement from the dreary and cool conditions that we experienced this weekend over much of the northeast, with mainly sunny skies and light winds throughout the day. A weak area of mid level ridging over the east provided adequate southwesterly flow, which ushered in highs ranging from the upper 70’s to middle 80’s across the area. This pleasant weather should last into the evening as a weak surface high pressure system associated with the mid level ridge begins to move off the Atlantic coast and into the West Atlantic. This will allow for winds from the south to persist into the evening, but conditions will be supportive for some radiational cooling to take place. Expect temperatures to drop into the lower 60’s to middle 50’s across the area, with locations well removed from the coast a good 5 degrees cooler.

This evenings latest high resolution GOES-16 visible satellite imagery, regional radar mosaic, and surface observations showing a rather tranquil and pleasant Labor Day (Courtney of Simuawips)

This evenings latest high resolution GOES-16 visible satellite imagery, regional radar mosaic, and surface observations showing a rather tranquil and pleasant Labor Day (Courtney of Simuawips)

Tuesday into Wednesday

Tomorrow should start off rather calm for much of the area, with partly cloudy conditions likely taking over by mid morning. A large upper level trough will be moving down from Canada and into the northern portions of the Northeast. This cold front will likely spark some showers and thunderstorms over portions of the Northeast during the afternoon hours, however this feature will likely take a while to reach the area. Otherwise, more strong south-westerly flow just ahead of the impressive trough will overspread the area. This will once again lead to warm mid level temperatures, which should be able to support highs into the middle to upper 80’s by late tomorrow afternoon. As with many high mid level temperatures/questionable cloud cover days, the areas that see more sunshine during peak heating will likely wind up a few degrees warmer than the areas that stay mostly cloudy. Precipitable water values and dewpoints will also begin to steadily increase during the day, and this will make for a more “muggy” feel to the day tomorrow with heat indices possibly reaching into the lower 90’s.

As we move later into the day, the cold front will begin to move to the east with time-likely setting off numerous showers and thunderstorms over Pennsylvania and New York. PWATS will be quite high just ahead of the front, and a very impressive upper level jetstreak will promote expansive upper level divergence, which will work to enhance convergence at the surface. Additionally, the upper level trough moving in will be quite large and powerful for this time of year, and will have some decent wind shear associated with it. When all these ingredients come together later in the day on Tuesday, very heavy rainfall will be possible with any showers or thunderstorms that develop west of the immediate NYC metro area. If a less-cloudy solution works out tomorrow, we could see instability rise over the area, which would be supportive for more strong-severe thunderstorms with strong winds, frequent lightning, small hail, and torrential downpours all possible.

These showers and thunderstorms should gradually work their way towards the NYC metro area by the mid to late evening hours tomorrow. The activity will likely be on the downswing due to a loss of daytime, so they will likely be below severe limits, even though gusty winds, frequent lightning and heavy rains will still be possible. There is a minor concern for flash flooding as the north to south orientation of the trough will allow for the showers to train over the same locations as the night goes on. The one positive thing about this scenario will be that the increased shear values will allow for the showers and storms to move rather quickly. This should limit the overall flood threat to roads and poor drainage areas.

By Wednesday morning, the cold front should be along the Mid Atlantic coast, but beginning to slow down significantly as it starts to bump into the west Atlantic ridge. The overall upper level trough will also begin to nudge up against the ridge and this should cause the associated upper level jet to expand and intensify as well. This will set the stage for a much cooler and unsettled day across the area as a Canadian airmass overspreads the area, and the lift from the impressive upper level jet provides support for showers and isolated thunderstorm development. Gusty winds will be possible with any of the stronger showers and thunderstorms, as they may be able to mix down stronger winds from high up in the atmosphere. Overall, expect temperatures to be limited to the middle 60’s across the area, which is a good deal below normal for this time of year.

There will likely be some residual rain on Thursday, with the core of the trough passing nearby. We will have more on this and this weekends conditions on Wednesday!

This afternoons NAM model showing the expansive full-latitude trough moving in and over much of the East.

This afternoons NAM model showing the expansive full-latitude trough moving in and over much of the East.

Hurricane Irma Update 

Hurricane Irma has intensified this afternoon after a Hurricane Hunter flight investigating the storm found winds up to Category 4 strength (130mph). The storm appears quite healthy on this afternoon/evenings satellite imagery , with very deep convection firing within the eyewall of the storm and upper level outflow expanding outward from the hurricane. The presence of upper level cirrus clouds has even increased in the northern half of the system, which has been lacking over the past two days due to a cutoff low pressure system imposing some northerly winds onto the system. Regardless, the system appears to be in a conducive environment for further strengthening over the next few days , characterized by low shear, very warm sea surface temperatures, and little to no dry air in the vicinity.

Irma will be moving towards the northern Leeward islands, with tropical storm conditions possibly affecting the area as early as tomorrow night. Irma will likely be a strengthening Category 4 hurricane by that time, and conditions are likely to rapidly deteriorate as it moves closer. The models have converged on the idea that the center of Irma will be over the US Virgin Islands  during the day on Wednesday, and will likely bring extremely strong sustained winds, torrential downpours, life-threatening mud slides, as well as very dangerous waves/surge. With 36 hours left until direct impacts are felt, those in this area should rush preparations to completion as soon as possible! A Hurricane Warning has been issued for most of the northern islands, with a Hurricane Watch in effect for Puerto Rico.

12z HWRF showing a very dangerous Hurricane Irma over the northern Leeward Islands (Valid 8am Wednesday)

12z HWRF showing a very dangerous Hurricane Irma over the northern Leeward Islands (Valid 8am Wednesday)

Irma will likely move to the north of Puerto Rico late Wednesday, likely bringing tropical storm, to even hurricane conditions to the island. The hurricane will likely remain an extremely dangerous storm through this time, much of the same hazards-if not all apply. Irma should begin to move away by early Thursday morning and will likely continue heading west-northwest, just north of Hispaniola. This is around the point that some models begin to diverge on the exact track of Irma, with some keeping the storm moving towards the west and into the southern Bahamas, and others showing a stronger mid level ridge over the system attempting turn the hurricane a little south of due west and into Cuba. This will have to be monitored over the next few days, due to the fact that Irma would likely weaken a good deal if it were to interact with the mountains of eastern Cuba (which would have some impact on the eventual track). Interestingly enough, the later part of the forecast seems to be much clearer than it originally was, with multiple models and their ensembles showing Irma lifting north once its near the Cuban coast by this weekend. The main question will be just how far west does the storm get before its begins to move north? With near-continuous observation by NOAA and USAF planes, special soundings, and the activation of Critical Weather Days, we will be getting a massive amount of data ingested into the models that should help with the forecast of the next week or so.

Regardless, it can be said that there is an increasing hurricane threat for portions of south Florida, and residents in that area should closely monitor the progress of Irma over the next few days and begin to review their hurricane plans. 

Category 4 Hurricane Irma over the Central Atlantic this evening as seen by GOES 16.

Category 4 Hurricane Irma over the Central Atlantic this evening as seen by GOES 16.

We will have more on Hurricane Irma on Wednesday!

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Have a great evening!

Steve Copertino

 

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Dual Rain Threats This Week, Tropical Storm Gert Intensifying Off the East Coast

Good Evening! 

Today started off decently clear and warm over much of the area, but as the day progressed onward, the elongated area of high pressure just to our south began to move offshore. As it did so, this allowed low level moisture and cloudiness to begin to filter over the region, but still allowed conditions to remain slightly below-average, with highs locked in the upper 70’s to lower 80’s. As of this evening, cloudiness has begun to increase in earnest across the area in response to an impulse of mid level energy working its way north and east along mid level trough. In addition to cloudy skies, this impulse of energy has also sparked some showers over the northern portions of the Mid-Atlantic, with sections of Maryland, Delaware, Pennsylvania, and southern New Jersey all reporting light to moderate showers moving across that area this evening. This area of showers should continue to head east-northeast over the next few hours, but may have trouble making too much northern progress as there is some residual mid level dry air over portions of northern NJ and Long Island. This mid level dry air has also been noted on this evenings radar, as numerous areas of virga (rain not able to reach the ground due to dry conditions) popped up and quickly dissipated soon after.  Overall, conditions should remain cloudy with a chance of a light shower the further south you go, but with increasing moisture, light southerly winds, and increasing clouds at all levels-radiational cooling will be very hard to come except for locations in northern Pennsylvania as well as central New York. This will keep low temperatures in the mild range of the upper 60’s to lower 70’s, with temperatures around 5 degrees cooler to the north and west.

This evenings latest high resolution GEOS 16 visible satellite imagery, regional radar mosaic, surface observations, and WPC frontal locations.

This evenings latest high resolution GEOS 16 visible satellite imagery, regional radar mosaic, surface observations, and WPC frontal locations.

Tuesday Through Friday 

Tuesday morning will likely start off with numerous clouds and possible showers over the region, and another shortwave trough begins to move just to the southwest of the area, bringing another new batch of mid level instability and moisture. At this time, it appears that the best chance for steady rain will be tomorrow morning, likely over the southern portions of the New York Metro area, with locally heavy areas of rainfall possible. As the day progresses, the steadiest rain should begin to head east and off the Mid Atlantic coast. This will likely give way to improving conditions by the mid afternoon hours, with some clearing possible the further away from the coast that you area. With the mid level still feeding moisture in from the south and east, any clearing will likely allow for some instability to build up. Though we will have some instability and weak wind shear to work with tomorrow over the interior, the models indicate an area of sinking air associated with a dissipating mid level system to our north. This should greatly reduce the potential for thunderstorm coverage, but in general isolated shower and thunderstorm development is likely across portions of New York and Pennsylvania tomorrow afternoon and into the evening hours. With the lack of severe parameters coming together, the overall threat for severe weather should be quite low tomorrow, but some stronger storms could produce gusty winds, very heavy rainfall, and even small hail.

As we get closer to New York City, cloud cover and much more stable/sinking air over the region should generally limit and thunderstorm development through the evening hours, and any storms that track close to the area should be on the weakening trend and will likely die-off. With winds coming off of the Atlantic, tomorrow evening will likely be another mild and somewhat-muggy one as lows will likely stay in the low 70’s to upper 60’s across much of the area.

Wednesday should be a much more pleasant day across the Northeast, as dry air behind the mid level disturbance begins to overspread the area, knocking out much of the cloud cover during the early morning hours of the day. Mid to upper level ridging will allow for temperatures on Wednesday afternoon to get quite warm, with highs likely reaching up into the upper 80’s and into the lower 90’s across the region. Few clouds are expected through the evening hours, as a backdoor coldfront pushes from north to south across our area, working to lower dewpoints region-wide.

Thursday looks to be relatively nice for the majority of the day, as the backdoor coldfront halts its progress around the Mid Atlantic region, keep the area warm, but less humid during the day. With dry northwesterly flow established, conditions should be mostly clear across the area. This looks to change later in the evening, as a large mid level system over the Great Lakes looks to approach the Northeast after sunset and into Friday. This system will be accompanied by a strong cold front, which could be responsible for shower and thunderstorm development late Thursday and into Friday, but at this time, it does not appear that this system will carry much of a severe weather threat as well as a flooding threat. This will likely have to be reassessed later in the week, so check back for updates!

This afternoons NAM model showing the progression of Tropical Storm Gert off the east coast, as well as a mid level system over the central part of the county, which may work to bring showers and thunderstorms over our area later this week,

This afternoons NAM model showing the progression of Tropical Storm Gert off the east coast, as well as a mid level system over the central part of the county, which may work to bring showers and thunderstorms over our area later this week

Tropical Storm Gert Nearing Hurricane Intensity 

As of 5pm this evening, Tropical Storm Gert was located roughly 450 miles to the west-southwest of Bermuda, and moving north at around 8 miles per hour. Gert has taken advantage of a relatively favorable environment today characterized by low vertical wind shear, very warm sea surface temperatures, moist air, and slow storm motion. This allowed the storm to develop intense thunderstorms near the core of the system, which in turn began a period of intensification to just below hurricane status-at 70 mph. Recent visible satellite images from the GOES-16 satellite showed that the cloud tops of Gert were warming a little, maybe indicating a brief halt in the intensification process, but with the storm located over very warm water and under a favorable environment, it appears quite likely that Gert will become a hurricane within the next 12-18 hours.

Gert will continue to track to the north as it rounds the western edge of the Bermuda high tomorrow, likely continuing to strengthen as it does so. Gert will likely begin to accelerate and take on more of an easterly component later tomorrow, as a shortwave trough moves over the Northeast. As the storm begins to interact with the shortwave trough over the northern Atlantic ocean, it will likely begin its extra-tropical transition by late Wednesday. Thereafter, the storm is likely to remain a powerful extra-tropical system, which may eventually threaten portions of Europe further down the line. Impacts for the east coast will be limited to increased wave swells and a high risk of rip currents. The main risk from Gert will be help by any maritime craft venturing off the east coast this week.  Elsewhere in the Atlantic, there is an area of disturbed weather located in the far eastern Atlantic which may try to gradually develop into a tropical cyclone over the next few days as it heads generally WNW at 15mph.

GOES-16 visible satellite imagery of Tropical Storm Gert off of the southeastern coast of the US this evening (Courtesy of simuawips.com)

GOES-16 visible satellite imagery of Tropical Storm Gert off of the southeastern coast of the US this evening (Courtesy of simuawips.com)

For more information and posts like this one, make sure you sign up for Premium Forecasts — where multiple detailed articles, videos, and interactives are posted each day. Also, come interact with our staff and many other weather enthusiasts at 33andrain.com!

Have a great evening!

Steve Copertino

namconus_z500_vort_neus_37

Pleasant Weather Today, Isolated PM T-Storms Tuesday, More Unsettled Late Week

Good Morning and Happy Monday! Today will be another pleasant warm day. This will allow for a return flow and more mid-high level clouds to filter and mix with sunshine as the day goes on. Humidity will also increase a little bit later this afternoon. But overall it will be pleasant warm summer day, with high temperatures in the lower to middle 80s this afternoon. A light southeast flow may keep temperatures slightly cooler along the shore.

Partly cloudy skies are expected through tonight  A weak upper-level disturbance will be moving through early tonight. But there will be little or no instability tonight. So only a slight chance for some isolated showers. Most areas will be dry. Some areas of patchy fog may also develop late tonight, especially along coastal areas, as onshore flow enhances low-level moisture underneath inversion. Cloud cover will keep temperatures warmer tonight. Low temperatures will likely be in the lower to middle 60s over the Interior areas and in upper 60s to near 70 over more urban and coastal areas.

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PM Update: Briefly unsettled weather continues in the Northeast

Good evening and Happy Friday! An active weather day continues across much of the Northeast States. Despite a lack of organized severe weather or widespread impactful hazardous conditions, scattered thunderstorm coverage throughout the Northeast part of the country has created issues, specifically in regards to air travel. Significant delays were reported this evening in many major Northeast US airports as a result of the showers and storms.

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