A Weakening Bud And Invest 91L

Oh how the mighty have fallen! Yesterday, Bud was a hurricane. Today it is a tropical storm with 50 mph 44 knots 80 km/h winds. It was once a formidable Category 3 hurricane. All the forecast models have Bud weakening.

With Bud running into cooler water and closer to land, it is most likely to weaken. The next important question is where Bud goes.

The forecast models are having Bud moving towards Baja California and the Southwestern US as a low pressure system. The moisture from Bud is certainly welcomed in the Southwest as they are very dry.

Almost the entire Four Corners is engulfed in a severe drought. It centers around where the Four Corners meet. There is also a severe drought in the Texas Panhandle region. Any rain is welcomed regardless. This leads to Invest 91L in the Caribbean. Many are asking where 91L will go.

Most of the forecast models have Invest 91L heading towards either Mexico or Deep South Texas. Some have it heading towards Southeast Texas. Regardless of where 91L goes, rain will be the main issue. Since Invest 91L is over an area of warm water, does it have a chance of developing?

Most forecast models have 91L at tropical wave or tropical depression. One has it as a tropical storm. Again, it is too early to tell if it will develop. Tropical waves or low pressure areas in the Caribbean and Gulf of Mexico can form suddenly into a tropical storm or even hurricane. It has happened many times in the past. I am not suggesting it will happen with 91L. It is something to consider.

The Tropical Cyclone Formation Probability Guidance Product does give Invest 91L a chance of developing into a tropical cyclone in the next 48 hours. Again, that is only a small chance of developing.

Since, we are on the topic of tropical weather trouble, it brings rain. Various forecast models have different rain amounts, which are from GFS, Canadian, EURO, and Weather Prediction Center (WPC). They are from Weather.US and Weather Prediction Center (WPC)-Quantitative Precipitation Forecasts (QPF). These are 7 day rainfall totals.

The GFS has less rain for Texas and the Southwest. Southeast Texas has 2 to 4 inches of rain. The Southwest sees 0.50 to 2 inches of rain with 6 inches in the mountains.

The Canadian is not particularly generous for the Southwest. However for Southeast, Texas it has up to 8 inches of rain.

The EURO is generous for Southwest and Texas. The mountains of Arizona, New Mexico, and Colorado have up 8 inches of rain. Most of Arizona is wet as well compared to GFS and Canadian.

The WPC has 2 to 4 inches of rain over Southeast Texas. The Southwest has 0.50 to 1 inches of rain with isolated areas seeing 2 inches of rain.

The forecast models are unanimous on that rain will fall in Texas and the Southwest. They diverge on rain amount. Some forecast lesser amounts, while others forecast higher amounts. We should have a better idea of rain amounts later on.

My take on this. Invest 91L is more likely going to be a rain event. I do not expect 91L will develop at this point, but of course anything can happen. I do not think we will see another Harvey event from 91L. It is not forecasted to linger over Texas, like what Harvey or Allison did. As for Bud, the Southwestern US should welcome the rain with open arms. They will need it for sure.

The forecast models came from NCAR-Tropical Cyclone Guidance. The GIS drought map is from United States Drought Monitor.

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Hurricane Bud And Invest 91L

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It is June and the tropics are heating up. We have two areas of interests, Hurricane Bud in the East Pacific and Invest 91L in the Caribbean. Let’s start with Bud.

Hurricane Bud was a powerful Category 3 hurricane that weakened into a Category 2 hurricane with 100 mph 85 knots 161 km/h winds. It is due to cooler water Bud is encountering. Cooler water tends to weaken hurricanes even if there is not a whole of wind shear.

The area of warm water in the East Pacific is not that great. However, two major hurricanes have formed so far, which are Aletta and Bud. East Pacific is one of the most active basins despite its small size. As Bud weakens, where does it go? Here is a heat map forecast for Bud.

Most forecast models have Bud heading towards Baja California later by the end of the week. Where it goes after looks to be heading towards the Southwest. They can certainly use the rainfall as they are in a severe drought. The next question is how strong will Bud be?

Most forecast models have Bud as a tropical storm with one as a Category 1 hurricane around the time it us close to Baja California. From there, it is forecasted to weaken to a tropical depression.

The next problem is closer to home, Invest 91L. It is located off the coast of Honduras in the Caribbean. It is right now just a tropical wave with a cluster of thunderstorms. Many are wondering where will 91L will go? Here is a heat map forecast for 91L.

Most of the forecast models have 91L heading towards the Western Gulf of Mexico. One has it heading towards Florida looping around. It is just one forecast model. The forecast models at this time are heading towards Texas. Since this is a tropical wave, the forecast model is subject to change. The $64,000 question is will 91L become a tropical storm or hurricane, which would be Beryl.

Most forecast models keep 91L at tropical depression. Only one has a tropical storm at this time. Intensity forecast models are unreliable, especially if nothing has developed yet. Some factors do favor development. Let’s look at the water around Invest 91L.

The depth of warm water in Caribbean and Gulf of Mexico is great and over a large area. The heat potential is fairly high in the Gulf of Mexico and Caribbean. Warm water is certainly a factor in tropical development, but not the only one.

Wind shear over the Gulf of Mexico is within average and looks to be trending downward. Less wind shear is more favorable for tropical development. If there is strong wind shear over warm water, tropical development is greatly reduced as they blow tops of thunderstorm clouds that forming into something tropical.

At this time, I do not think Invest 91L will develop. It looks to be more of a rainmaker. However, anything can change between now and the end of the week.

The forecast models came from NCAR-Tropical Cyclone Guidance. The tropical heat came from A href=http://www.aoml.noaa.gov/phod/cyclone/data/go.html>Tropical Cyclone Heat Potential (TCHP). Wind shear map came from Tropical Cyclone Formation Probability Guidance Product.

The Average Tropical Cyclone Eye Size, ROCI, and Ambient Pressure

Let’s start with the Atlantic Basin. This is from 1988-2010 Best Track for Atlantic Hurricane
1988-2010 Best Track for Atlantic Hurricane

Eye Size
Mean
23.1 Nautical Miles (nm)

Median
20 nm

Standard Deviation
10.9

Smallest
5 nm (I do not know what is up with this, but the Best Track lists Wilma’s eye as 5 nm, even though the actual size was 2 miles or 1.7 nm)
Wilma 10/19/2005 1200 UTC (Z)

Largest
90 nm
Ophelia 9/13/2005 0000Z

Ambient Pressure
Mean
1011.1 Millibars (mb)

Median
1011 mb

Standard Deviation
2.96

Lowest
988 mb
Earl 9/5/2010 0000Z

Highest
1032
Isidore 9/28/1996 0600Z

Radius of the Outer Closed Isobar (ROCI)
Mean
186.4 nm

Median
180 nm

Standard Deviation
65.1

Smallest
30 nm
Iris 9/20/1989 0000Z

Largest
555 nm
Gilbert 9/12/1988 1200Z

Here is the East Pacific, which is off the West Coast of Mexico.
For the East Pacific.

From 2001-2010 Best Track for East Pacific Hurricane
2001-2010 Best Track for East Pacific Hurricane

Eye Size
Mean
16.7 nm

Median
15 nm

Standard Deviation
8.2

Smallest
5 nm (There are probably East Pacific Hurricanes with smaller eyes.)
Juliette 9/24/2001 0600Z

Largest
75 nm
Douglas 7/24/2002 0000Z

Ambient Pressure
Mean
1009.2 mb

Median
1009 mb

Standard Deviation
1.6

Lowest
1000 mb
Blanca 6/23/2003 0000Z

Highest
1017 mb
Fausto 9/3/2002 0000Z

ROCI
Mean
166 nm

Median
160 nm

Standard Deviation
45.7

Smallest
10 nm
Blanca 6/23/2003 0000Z

Largest
340 nm
Jimena 8/31/2009 0000Z

Here is a graph for mean and median.

Mean

Median

Based on the statistics, Atlantic storms are larger than East Pacific. No surprise that the Atlantic Basin is much larger than the East Pacific Basin because there is cooler water to the west towards Hawaii. However, in El Nino years, the waters of East Pacific is more favorable, which means tropical cyclones last longer and can even travel into the Central Pacific and West Pacific as it happened with Hurricane John in 1994. The East Pacific is one of the most active basins in the world.