Month: August 2014

Very Warm & Humid Through Labor Day with Heavy Thunderstorms Likely

Miguel Pierre Flooding, Severe Wx

A deep southwesterly flow, will transport a very warm and humid airmass today with clouds mixing with some sunshine. High temperatures today will depend on the amount of cloud cover. Areas that see more sunshine, could get make run at 90 degrees or higher today. More clouds than sun, highs will be in lower to middle 80s. The forecast highs will compromise between middle to upper 80s. Except near the shore, a southerly winds likely keep high temperatures in lower to middle 80s. A surface trough and shortwave trough (upper-level disturbance) will trigger numerous showers and thunderstorms across the region late this afternoon and tonight.

6z NAM showing a surface temps middle to upper 80s in most areas with dews in 60s (top left). Also a shortwave trough approaching trigging showers and thunderstorms west of New York City
6z NAM model showing a surface temps middle to upper 80s this afternoon in most areas with dews in upper 60s and lower 70s , Also a shortwave trough approaching trigging showers and thunderstorms over Western parts of region late this afternoon.

Models show anywhere between 1000 J/kG and 2000 J/kg of MLCAPE with 25kt to 35kts of shear this afternoon and early this evening. This will support some thunderstorms to become strong to severe with damaging winds being the main threat. Some backing of the low-level winds this afternoon, could support an isolated, weak tornado. Especially over Northern NJ and Lower Hudson Valley. Some hail is also possible out thunderstorms. But threat for large hail is reduced somewhat with high freezing and wet-bulb zero levels. Inhibiting factors for severe weather today, are weak mid-level lapse rates and some cloud cover keeping surface-based instability from reaching extremely high levels. Also with winds more out the south this afternoon, areas near the coast will be more stable and this may cause thunderstorms to weaken. Which is why the Storm Prediction Center has the 15% slight risk northwest of NYC. Overall I’m expecting any severe weather reports to be isolated to scattered across to the region.

6z NAM model showing MLCAPE between 1000 J/kg and 2000 J/kg by early this afternoon over the Tri-State area.
6z NAM model showing MLCAPE between 1000 J/kg and 2000 J/kg by early this afternoon over the Tri-State area.

More likely than the severe weather, is potential for heavy rainfall out of thunderstorms late this afternoon and tonight with pwats (precipitable water values) near or over 2.00″.  With mostly unidirectional shear, some of training of storms with flash flooding possible in  low-lying or poor drainage areas. Depending how showers and thunderstorms setup some places could receive less than .50″ rainfall to locally one to three inches of rain.

6z NAM showing (pwats) precipitate water values 2.00" over greater over the Tri-state area
6z NAM showing (pwats) precipitate water values 2.00″ over greater over the Tri-state area

That all being said, it is not necessary to cancel plans. It will be dry, until late this afternoon for most areas and perhaps until early this evening for coastal areas. If you are at beach, park,pool, etc, be prepared to move indoor as quickly as possible, if a thunderstorm hits. Any thunderstorm whether severe or not, can produce dangerous cloud to ground lightning. Don’t take shelter under trees, as they are huge conductors of electricity. Tomorrow (Labor Day) will continue very warm and humid with mixture of sunshine and clouds. More scattered showers and thunderstorm will still be threat all day tomorrow. As the shortwave trough lingers over the area. Pwats still over 2.00″ will  support heavy rainfall out of any thunderstorm tomorrow. However, with move convective debris or clouds, this will likely keep instability lower. On Tuesday, surface high pressure will build briefly more sunshine. A deep southwesterly flow with 850mb temperatures around 18C will help temperatures rise into the lower 90s, away from the coast. A cold front and upper-level trough approaching from the west will trigger more showers and thunderstorms by Tuesday night.

Check the latest Tri-State 7-day forecast details and summary for more updates for today’s severe threat threat.

Also follow @WeathergunNY for any watches and warnings later this afternoon and night.

Have a nice Labor Day weekend!

Some Heat Returns, Labor Day Weekend Looking Unsettled

Miguel Pierre Severe Wx, Summer Wx, Uncategorized

Some heat is making comeback this week, as ridge builds over the Eastern US. This ridge has been enhanced by Cristobal. Which is now a category 1 hurricane just northwest of the Bahamas and will recurve out to sea this week. Today we saw sunny skies with highs in the middle to upper 80s through much of the local tri-state area. Tomorrow looks pretty same, except a stronger south to southwest flow may keep areas near the shore a little cooler tomorrow.

On Wednesday a cold front will be across the region, during the afternoon. The flow will turn more west to southwest, pumping in more heat and humidity. Temperatures with enough sunshine could get to or above 90F degress for highs on Wednesday for much of NJ and NYC area. Some showers and thunderstorms may form along this cold front. The NAM shows very unstable airmass away from the coast, with MLCAPE values between 1500 J/kg and 2500 J/kg. Shear is also marginal enough for threat of some isolated strong to severe thunderstorms. Other models such as GFS and ECMWF have the atmosphere more capped and stable, keep coverage of showers and thunderstorm very low. It should become clearer tomorrow if we are looking at threat of severe weather.

After this cold passes through Wednesday night, a cooler less humid airmass will be ushered in again. Higher temperatures return to near normal, in the lower 80s for most spots. Heat and humidity may try to return over the Labor Day weekend. As a ridge starting building east again. However, a frontal system approaching the west, may keep unsettled weather conditions for the weekend. At this time, it doesn’t look a like complete washout, and I don’t advise to change any plans yet. But there will probably be some showers or thunderstorms, at some point. Model guidance shows different timing of this system’s warm and cold front moving through the area. This should become clearer as we draw closer.

 

Tropical Storm Cristobal: No Threat Likely to the US

Miguel Pierre Tropics, Uncategorized

Tropical disturbance invest 96L was upgraded to tropical depression late yesterday. Then upgraded to tropical storm this morning with maximum sustained of 45mph and it is currently moving NW at 9mph. The storm is still most likely to gradually recurve away from the US, as it begins to feel influence of troughiness or a weakness in subtropical ridge over the Western Atlantic. Cristobal is now under a light shear environment with base of trough to the north. It is also moving over sea-surface temperatures near 26C-30C. This will allow for more strengthening today and tonight. These favorable conditions are likely to persist into middle of this week and Cristobal is likely to become a hurricane. The only impacts expected are some high waves and rip tides along the US East Coast this week.

CIMMS Shear Tendency Analysis at 12z showing light shear over Cristobal (the L)
UM-CIMMS Shear Tendency Analysis at 12z showing light shear over Cristobal (L)

This storm going as pretty much going as I had wrote about in my last post Some models over the last 48 hours waffled between a track over Florida/Gulf of Mexico and recurve farther east into the North Atlantic. But now that there is a more defined and deeper center of circulation and actual data on the extent of troughiness over the Western Atlantic, the model consensus is back with a recurve away from the US East Coast. Despite the model differences and media hype, this has remained the most likely scenario here all along. This is due to the pattern recognition and past experience with tropical cyclones. The ECMWF operational model, often most reliable and was the most consistent with this solution in the medium range. Unfortunately, it is not on many of spaghetti model plots that are used or shown around the media. The ECMWF ensembles had many members still showing a tropical wave being steered by low-level easterly flow into Florida/Gulf of Mexico. This is clearly not correct anymore.

0z ECMWF showing Cristobal being captured by new upper-level trough and into the North Atlantic
0z/25 ECMWF from PSU Ewall showing Cristobal being captured by a late week upper-level trough late and tracking out into the North Atlantic
today's 12z guidance showing a recurve out to sea this week:
Today’s 12z early guidance showing a recurve out into the North Atlantic this week

Cristobal will also be enhancing  and warmth over local Tri-State area this week. Temperatures may approach 90 in some spots, by Wednesday or Thursday with sunshine, a westerly flow, 588dm+ 500mb heights and 850mb temps near 18C. Humidity will be on the increase as well. However, this heat and humidity will likely be short-lived again, with another deep trough and cold front approaching from the west at the end of the week. Temperatures will likely return near to below normal next weekend. Long-range guidance shows the ridge building east again during the first week of September. But will have too see how much Cristobal influences the NAO pattern after this week, which could have an impact. Multiple times this summer we’ve seen long-range guidance show prolonged heat or warmth, only to have it muted as we get closer.