Hello, Dolly; so long, Bertha; Cristobal keeps on chugging along

Tropical Storm Cristobal continues to chug along the coast of North Carolina, dropping welcome rains over the eastern portion of the state. Morehead City radar shows a well-organized storm with plenty of spiral bands of thunderstorms. These bands have only moderate amounts of rainfall, which is fortunate, since Cristobal is moving so slowly. Rainfall amounts from Cristobal have generally been below two inches over eastern North Carolina, with one isolated pocket of four inches just north of Wilmington, NC. Cristobal is over waters of about 27°C, a degree above the threshold of 26°C needed to sustain a tropical storm. Wind shear is about 10 knots over the storm, and is forecast to fall below 5 knots by Monday. There is some dry air at mid and high levels that is interfering with Cristobal, contributing to the storm's relatively low rainfall amounts.

The expected decrease in wind shear may allow Cristobal to intensify to a 60 mph tropical storm by Monday, but conditions do not appear favorable enough to allow the storm to reach hurricane status. None of the models forecast that Cristobal will intensify beyond a 60 mph tropical storm. Cristobal will likely cause minimal or no damage to North Carolina. Cristobal will likely bring winds below 25 mph to Southeast Massachusetts and Nantucket Island on Monday night. However, these regions are likely to receive 2-4 inches of rain from the storm as it zooms by. The HWRF model predicts heavy rain in excess of four inches along the coast of Maine from Bar Harbor to the Canadian border from Cristobal's remnants on Tuesday. Lesser rainfall amounts of 2-4 inches are expected over Nova Scotia.

Links to follow:
Morehead City, NC radar
Southeast U.S. Marine observations and forecasts
Cape Hatteras, NC weather


Figure 1. Visible satellite image of Dolly and Cristobal at 1:02 pm EDT Sun July 20, 2008. Image credit: NASA GSFC.

Hello, Dolly!
Wind shear finally relaxed enough over the Western Caribbean today to allow Tropical Storm Dolly to form. Satellite loops show a large area of intense thunderstorms lies to the north of >Dolly's center, and these thunderstorms will bring heavy rains of 4-8" today and tomorrow to the Cayman Islands, Western Cuba, and the northern Yucatan Peninsula, including Cancun and Cozumel. This morning's QuikSCAT pass shows a large are of tropical storm force winds affecting the Western Caribbean. There was no closed circulation at the time of the QuikSCAT pass, but the Hurricane Hunters have since found a closed circulation, which one can also see on visible satellite loops. Heavy thunderstorm activity is now starting to build near the center of Dolly, which is the hallmark of an intensifying tropical cyclone.

The upper-level low that prevented Dolly from developing a closed circulation has weakened considerably over the past day, and will continue to weaken and slide southwestward out of Dolly's way today. This will create a low-shear environment for Dolly to intensify in. With very warm waters of 28.5°C ahead of it extending to great depth, Dolly is expected to intensify right up until landfall tonight over the Yucatan Peninsula. It is unlikely Dolly has time to reach hurricane status today, but a 60 mph tropical storm is possible tonight at landfall. Passage over the Yucatan will disrupt Dolly, which should need a day or so to recover once it emerges over the Gulf of Mexico. Steering currents will weaken once it does emerge, and Dolly will probably have at least two days over the warm waters of the Gulf before making landfall near the Texas/Mexico border Wednesday night or Thursday morning. This may allow Dolly to intensify into a Category 1 hurricane over the Gulf of Mexico, as predicted by the GFDL model. Rainfall amounts at landfall in Texas and northern Mexico are predicted to be in the 2-8" range, according to the HWRF and GFDL models.

Links to follow:
Cozumel, Mexico weather
Buoy 42056

So long, Bertha
Bertha is finally dead, and is now a powerful extratropical storm over the North Atlantic. The remnants of Bertha are expected to deliver tropical storm force winds to Iceland on Monday. Bertha set the record for the longest-lived July hurricane on record (and the longest-lived hurricane so early in the season). Bertha was a hurricane 7.75 days, which eclipses the previous record of 7 days held by Hurricane Emily of 2005. Bertha was also the longest-lived tropical storm on record for July (and for so early in the season), 17.25 days. Bertha was also the farthest east forming tropical storm and hurricane for so early in the season.

Elsewhere in the tropics
Three of our four reliable computer models for are predicting a new tropical depression will develop off the coast of Africa 3-5 days from now.

I'm not sure, but today might mark the first time on record that we've have three named storms on the same day in July in the Atlantic. The year 2005 came close, when Dennis and Emily existed on July 11, and Cindy's extratropical remnants were over New England.

I'll have a full update Monday morning.

Jeff Masters