Hurricane Sally Poised to Weaken

This morning’s visible satellite images were promising and Sally did intensify rapidly over the course of the day. However, the storm is now taking on shear and dry air is poised to infiltrate its entire core. This should halt strengthening and could even bring weakening over the next 6-12 hours.

Visible satellite image over the Gulf of Mexico showing Hurricane Sally with dry air wrapping around the SE quadrant of the inner core of the storm. Image valid for 9/14 at 21:15 UTC

Notably, however, the storm has another 24 hours over the warm waters of the Gulf of Mexico and could shrug off the dry air and shear and intensify again in the 12-24 hour period. Still, because of this dry air I am bringing down my maximum potential intensity to 110 mph, 970 mb (down from 115 mph, 965 mb). No changes to storm surge and freshwater flooding, which will be devastating across large portions of Mississippi and Alabama.

Coupe

Update: Hurricane Sally

16 UTC UPDATE: Aircraft reconnaissance has indicated that Sally is intensifying quite quickly. This was anticipated, given this morning’s visible satellite images, but central pressure has suddenly dropped to 985 mb with maximum sustained winds up to 85 mph.

The forward motion of this storm (6 mph) is extremely slow and indicates a long-duration water threat along the Gulf Coast. Depending on how much additional strengthening can occur, the wind threat will continue to grow along the Gulf Coast east of New Orleans.

Be sure to use National Hurricane Center forecast products to make important decisions regarding life and property.

Coupe

The Intensification of Tropical Cyclone Sally

Sally remains a tropical storm with maximum sustained winds of only 65 mph and and a minimum central pressure of 994 mb. While it currently resides in the bathwaters of the Gulf of Mexico, it has clearly been impacted by moderate shear over the last 24 hours. This hindered the anticipated steady intensification to a hurricane.

That is, until this morning. The first visible satellite images from Sally this morning strongly indicate that Sally will undergo its most steady period of intensification yet. Maybe not quite rapid intensification, but this morning will mark a turning point in the transition of Sally from a high-end tropical storm to a formidable hurricane that will inundate portions of the Gulf Coast east of New Orleans.

Visible satellite image of tropical cyclone Sally in the Gulf of Mexico

The forward motion of Sally is expected to stall as it approaches the Gulf Coast. Precipitation forecasts indicate a high likelihood of flash flooding across a broad area:

The maximum windspeed attained by Sally is not as relevant as the storm surge and precipitation, but for what it’s worth, I would cap Sally’s maximum potential intensity at 115 mph, 965 mb.

Coupe

Sample 5k Forecast

Unfortunately, the COVID-19 pandemic continues to cause race cancellations deep into the Fall 2020 racing season. As a demonstration of the product I can deliver to improve a race director’s situational awareness of weather factors potentially hazardous to volunteers and participants alike, I will post a series of forecasts, assuming a 5k will take place this Saturday August 22, 2020 starting at 9 AM. The location of the race will be in Three Bridges, like for the annual Three Bridges 5 miler race that we time.
I will provide a 5-day forecast on Monday morning with a big picture forecast of the general conditions to be expected for that morning. On Wednesday I will provide a 3-day forecast with more explicit timing of any potential weather hazards along with temperature, winds, and dewpoint, and any other variable necessary to assess racer comfort levels to inform the quantity of things the race often provides such as ice, water, shade, or on the other hand, cover from rain or shelter from cold. Finally, on Friday I will send out a 1-day forecast. A day-of forecast (0-day lead time) will only be sent out if high uncertainty was a factor in the 1-day forecast such as thunderstorms or a mesoscale convective system moving through the midwest overnight. In 2017, Tropical Storm Cindy moved through New Jersey and spawned a tornado in Monmouth County, only miles away from a race at CBA, causing a delay in the start of the race. This would require a 0-day lead time forecast, possibly in the form of a live phone call briefing with the race director within three hours before the race. A 0-day lead time forecast is only issued in these rare circumstances.

MONDAY MORNING FORECAST [5-day lead time]

The current forecast for Monday morning is dry and warm. A 5-day forecast will require the use of global ensemble numerical weather prediction models such as the GEFS and ECMWF and signals in 24-hour precipitation are the most useful at this leadtime to detect areas of disturbed weather.

Precipitation
Between 2am Saturday and 2am Sunday, there is a low probability of precipitation (<10%) accumulations greater than 0.01″ across most of New Jersey. However, there is a large precipitation signal around Florida which may indicate a stalled tropical wave or depression in the area. In the upper levels, an anomalously strong digging trough into the Gulf of Mexico will favor cyclogenesis to the east of Florida and an intensification of a SW to NE oriented upper level jet along the southeast coast. This moves north towards North Carolina through Tuesday but current steering patterns prevent it from moving towards New Jersey. There does not appear to be a major rain threat for Saturday morning from this system. The ECMWF indicates lower pressure over the Great Lakes region running up against the subtropical high pressure system over the southeast, but any precipitation from this system will lift north into Canada. The red polygon in the figure below shows the area with the lowest probability of precipitation on Saturday. The green colors over the area indicate the ensemble mean value of only 0.01 to 0.05″ of precipitation in the 24 hours from 2 am Saturday to 2 am Sunday, which is negligible and indicates an extremely low probability when all of the ensembles are assessed.

screenshot2323.png

In terms of temperature, there is a high confidence of above average temperatures. All ensembles suggest warm temperatures in the northeast, cool temperatures in the southeast, a dipole with a high likelihood of occurring given the upper level pattern. Dewpoints will remain consistent around 65F throughout most of the day, which isn’t as dangerous as it has been for a lot of the summer but with temperatures nearing 80F towards the end of the race, expect runners to be sweating out a lot of water and electrolytes. Above average temperatures during a morning race in August may pose heat related race hazards. Here are how temperatures will look as a function of time throughout the morning:

6am: 74F
7am: 75F
8am: 75F
*** race start ***
9am: 78F , sunny with a very light wind from the southwest.
*** first runner finishes ***
9:30am: 79F, sunny with a very light wind and will feel HOT.
10am: 81F, sunny. Most runners will have finished or will be finishing and it will feel HOT. Ensure water remains to help bring runners’ body temperatures down.
11am: 84F

Air temperatures nearing 80F, dewpoints in the mid-60s, and a negligible wind all contribute to more sweat and electrolytes that runners will lose during the race that will have to be replaced. Offering cold water and potentially cups filled with a sports drink with electrolytes at mile 3, or somewhere else near the halfway point may help combat runner lightheadedness and the need to vomit from rapid loss of fluid and/or electrolytes. Offering this at the finish line would also benefit runners and prevent post-race cramping, vomiting, and lightheadedness.

WEDNESDAY MORNING FORECAST [3-day lead time]

No update to the 3-day forecast is necessary from the 5-day forecast. All heat related hazards remain highly likely. and the likelihood of precipitation is again very low.

Coupe

September Hurricane Forecast

The Colorado State and NOAA hurricane forecasts call for near record number of tropical cyclones in the North Atlantic for the duration of the hurricane season (through November). Based on the August NMME forecast for global SSTs in September, broad La Nina-like cooling will be present along with near-record North Atlantic tropical SSTs, including into the subtropical North Atlantic. Both factors will bring about favorable environmental conditions for any TCs that do form. The unresolved question is how many situations for TC genesis arrive? Environmental conditions are only one factor – one needs sufficient convergence or simply a train of easterly wave disturbances. Some suggest a standing wave pattern over east Africa will generate these easterly waves through time and generate a number of TCs between August 20th and September 15th.

Screenshot from 2020-08-16 22-39-36.png

The week 3-4 CPC precipitation forecast (August 29th – September 11th, 2020) includes an above average precipitation signal for much of the southeast and Gulf Coast. This is undoubtedly a part of the signal for TCs impacting the US coast in this time frame. For forecasts into October, the signal of warming only gets worse. If an active period TC genesis does occur into October, it could be a long fall for the east coast.

Coupe, PhD

Verification for 1/30 to 2/1/31

Apologies for the short hiatus. The dissertation isn’t going to write itself

1/29 to 2/1 Climatology: Average high: 40F, Average low: 22F
Thursday 1/30/20 Verification: High of 37F and Low of 25F. (0F predicted vs +1F actual )
Friday 1/31/20 Verification: High of 42F and Low of 29F. (+3.5F predicted vs +9F actual)
Saturday 2/1/20 Verification: High of 45F and Low of 34F. (+8F predicted vs +9.5F actual); Coastal storm remained mostly offshore but a few bouts of light rain appeared throughout the day. Total precipitation accumulation of 0.01″.

January 2020 at Rutgers Gardens was remarkably warm compared to climatology. The entire month was 8F above the climatological mean. Only 1.8″ of snow was recorded, based on two events (0.6″ on 1/5 and 1.2″ on 1/18). Precipitation was slightly below normal at 1.99″ for the month. The lowest temperature recorded was 15F on 1/20 and the warmest temperature was 69F on 1/11.

Short Range

Overnight, don’t be surprised if there is a dusting of snow on the ground as a the base of a negatively tilted trough provides rising air on the west side of an area of low pressure that is moving out of the region. Snow accumulations may be as much as 0.5″ in far northern New Jersey but likely just a dusting in Central New Jersey. In very rural areas of New Jersey the low temperature may fall as low as 30F, so anticipate the possibility of light icing. Sunday Feb 2nd will be characterized by a shift from  W to SW winds as temperatures rise to 43F. After the sun sets there is another chance of a light dusting of snow as a weak area of low pressure moves through the area.

Long Range

Through 2/5/19, New Jersey will enjoy above average temperatures with low temperatures above freezing each day. The first significant cold front will move through late on 2/5, but mostly zonal flow will prevent the coldest air from moving south of central New York. A deepening shortwave and accompanying vorticity maxima on the eastward side of the trough will move through the northeast on February 7th, aiding an inland moving area of low pressure that will move northeast from the Gulf of Mexico, across the southeast, and along eastern PA. We will enjoy warm temperatures being on the warm side of this disturbance. Temperatures will remain mixed during the first two weeks of February as a ridge develops across the southeastern United States while cold Alaskan air spills across Canada, the western and central US.  A very strong midlatitude jet stream and a record strong AO (near 5 sigma) will prevent extreme intrusions of cold air through the first two weeks of February. Thus, temperatures will be moderate but likely will remain on the warm side.

During mid-February, the mid Atlantic will be right in the middle of a strong thermal gradient which may be favorable for unsettled weather. However, high latitude blocking is nowhere to be found, which will severely limit our ability to see the development of strong developing cyclones from 2/10 to 2/20. I mentioned a few days ago that the GEFS was showing the SPV becoming severely disturbed, but in recent model runs the SPV is now able to shrug this off mostly. The result is a SPV that is slightly displaced towards Greenland and extreme northern Canada. This shifts the coldest air over parts of North America but it is not far south enough to benefit us in the mid-Atlantic US. Winter is looking a little bleak, but it’s always possible to squeeze out some storms out of March if we can manage a sustained -NAO with cold air displaced over North America.

A look at the next four days of temperatures at Rutgers Gardens:
Sunday 2/2/20: High of 43F and Low of 34F. (+7.5F)
Monday 2/3/20: High of 49F and Low of 35F. (10.5F)
Tuesday 2/4/20: High of 53F and Low of 39F. (+14F)
Wednesday 2/5/20: High of 53F and Low of 32F. (+10F). Strong cold front moves through late in the evening. The morning low will actually not drop below 45F.

Coupe

Verification for 1/29/20

1/28/20 Climatology: Average high: 40F, Average low: 22F
Wednesday 1/29/20 Verification: High of 43F and Low of 33F. (+3.5F predicted vs 7F actual)

A look at the next four days of temperatures at Rutgers Gardens:
Thursday 1/30/20: High of 37F and Low of 25F. (-/+0F)
Friday 1/31/20: High of 42F and Low of 29F. (+3.5F)
Saturday 2/1/20: High of 45F and Low of 34F. (+8F); Potential coastal storm.
Sunday 2/2/20: High of 45F and Low of 34F. (+8.5F)

Coupe

Verification for 1/28/20

1/28/20 Climatology: Average high: 40F, Average low: 22F
Tuesday 1/28/20 Verification: High of 46F and Low of 34F. (+4.5F predicted vs 9F actual)

A look at the next four days of temperatures at Rutgers Gardens:
Wednesday 1/29/20: High of 40F and Low of 29F. (+3.5F)
Thursday 1/30/20: High of 35F and Low of 25F. (-1F)
Friday 1/31/20: High of 42F and Low of 29F. (+3.5F)
Saturday 2/1/20: High of 45F and Low of 34F. (+8F); Potential coastal storm.

Coupe