Boris Hits Mexico; Atlantic's First Invest of 2014 Forms in Gulf of Mexico

Tropical Storm Boris made landfall near 2 am EDT Wednesday in Southeast Mexico as a tropical storm with 40 mph winds. The storm has weakened to a tropical depression and is expected to dissipate later today, but Boris remains an extremely dangerous rainfall threat to the region. Reports from the Mexican Weather Service indicate that the city of Tonala on the coast of Chiapas has recorded 12.5" (318 mm) of storm-total rainfall, and NHC is calling for rainfall totals of up to 20" from the storm. Tropical Storm Agatha hit this region at the end of May 2010 as a weak tropical storm with 45 mph winds, and dumped up to 22.27" of rain. The resulting catastrophic flash floods and landslides killed 190 and caused $1.1 billion in damage, mostly in Guatemala. Heavy rains from the precursors of Boris triggered a landslide in Guatemala over the weekend, killing five people.

Heavy rains from Boris are not the only weather hazard Mexico is dealing with. A brutal heat wave with the hottest temperatures ever recorded in June scorched the northern Mexican states of Sonora and Chihuahua on Tuesday. According to weather records researcher Maximiliano Herrera, monthly records for hundreds of stations with almost a century of data were beaten on Tuesday, some by as much as 5°C (8°F). The capital of the Sonora state, Hermosillo, hit 121°F (49.5°C) on Tuesday, the hottest temperature ever recorded in the city. The previous June record was 45.5°C, and the previous all-time record was 48.5°C.


Figure 1. Latest satellite image of Invest 90L over the Gulf of Mexico, and the remnants of Boris over Southeast Mexico.

Atlantic's first "Invest" of 2014 forms in Gulf of Mexico
The National Hurricane Center's first area of interest in the Atlantic for 2014 was designated on Wednesday morning in the Southern Gulf of Mexico's Bay of Campeche. Invest 90L is nearly stationary, but satellite loops show that 90L is kicking up some heavy thunderstorms along the Mexican coast. Wind shear as diagnosed by the 8 am EDT Wednesday run of the SHIPS model was high, 20 - 25 knots, and wind shear is expected to stay high over the Bay of Campeche through Saturday. By Sunday, wind shear is predicted to drop, and 90L may have a better chance to develop then. Boris' remnants will be working their way northwards and arrive in the Bay of Campeche over the weekend, and the extra spin and moisture from Boris have the potential to aid development of 90L. However, a band of high wind shear associated with strong upper-level winds from the subtropical jet stream is predicted to lie over the Central Gulf of Mexico, and these winds may interfere with development. Sea surface temperatures (SSTs) in the Southern Gulf of Mexico are about 28°, which is about 0.5° above average. These warm waters do not extend to great depth, and the total heat energy available to intensify a potential storm is rather low. SSTs cool quickly as one goes to the north, are a marginal 26°C in the Central Gulf of Mexico. None of the reliable genesis forecast models predict that 90L will develop over the next five days. In their 8 am EDT Wednesday Tropical Weather Outlook, NHC gave 2-day odds of development of 10% and 5-day odds of 20%. I put these odds at 20% and 30%, respectively, given the propensity of the Bay of Campeche to spin up tropical cyclones in recent years.

What is an "Invest"?
When a National Hurricane Center forecaster sees a tropical disturbance that may be a threat to develop into a tropical depression, the forecaster may label the disturbance an "Invest" and give it a tracking identification number. There is no formal definition of what qualifies as an "Invest". Declaring an "Invest" is merely done so that a set of forecasting aids like computer model track forecasts can be generated for the disturbance. The "Invest" is given a number 90-99, followed by a single letter corresponding to the ocean basin--"L" for the Atlantic, or "E" for the Eastern Pacific. Other warning agencies assign "Invests" for the other ocean basins--"W" for the Western Pacific, "A" for the Arabian Sea, etc. Detailed microwave and traditional satellite images are available for all "Invests" across the globe at the Navy Research Lab web site.


Figure 2. On June 1, 2014, sea surface temperatures in the Gulf of Mexico were a very warm 28°C in the southernmost Bay of Campeche on June 1, 2014, but diminished quickly to 26°C in the Central Gulf. Image credit: NOAA/AOML.

Jeff Masters