Danny Dies; Erika Coming?

Tropical Storm Danny has met its demise at the hands of dry air and high wind shear, a victim of an El Niño-year atmosphere over the Caribbean that has been very hostile to hurricanes. The Hurricane Hunters were unable to find a closed circulation in Danny on Monday morning, and satellite loops and radar loops show that Danny's heavy thunderstorms activity has been steadily diminishing. Danny’s remnants will continue to head west at about 15 mph over the next few days, bringing heavy rains.


Figure 1. Radar image of Tropical Storm Danny's remnants from the Guadaloupe/Martinique radar, taken at 12:15 pm EDT Monday, August 24, 2015. Image credit: Meteo France.


Figure 2. Drought conditions in Puerto Rico as of the most recent issuance of NOAA’s Drought Monitor. Severe to Extreme drought covered all of eastern Puerto Rico, including the capital of San Juan. Image credit: National Drought Mitigation Center.

A drought helper, but not a drought buster for Puerto Rico
Danny’s remnants are expected to dump 2 - 4” of rain across portions of the drought-parched northeast Caribbean islands, which may cause localized flash flooding and mudslides Monday and Tuesday. However, these rains will not be enough to break the El Niño-driven drought that has gripped the region since this spring. Since January 1, Puerto Rico’s capital, San Juan, has received about ten inches of rain less than their usual 33” of rain. As a result, severe to extreme drought conditions have hit the region, with reservoir levels hitting their lowest levels in decades. San Juan and much of the northern coast of Puerto Rico are under water restrictions, where hundreds of thousands of households receive water only two days per week. The strong El Niño event underway in the Eastern Pacific has created an atmospheric circulation that has brought dry, sinking air to the Caribbean all summer, squelching thunderstorm activity during the traditional peak of the Caribbean rainy season. Central America is also suffering; in Guatemala, one million people are starving due to the drought, and in Honduras, ten municipalities are now officially experiencing famine.


Figure 3. MODIS image of 98L from NASA's Aqua satellite taken at approximately 9 am EDT Monday, August 24, 2015. Image credit: NASA.

98L in Central Atlantic could become Erika
In the Central Atlantic about 1200 miles east of the Lesser Antilles Islands, Invest 98L appears poised to become the next tropical depression of the 2015 Atlantic hurricane season, as it steams westward at a rapid 20 mph. Satellite loops on Monday morning showed that 98L had a well-developed spin and some low level spiral bands, but heavy thunderstorm activity was limited, due to dry air. The Saharan Air Layer (SAL) analysis offered by the University of Wisconsin shows plenty of dry air to the north and west of 98L, and this dry air will potentially impede development of 98L throughout the week. Sea surface temperatures (SSTs) are favorable for development, near 27°C, and will warm to 28°C by Wednesday. The 8 am EDT Monday run of the SHIPS model diagnosed moderate wind shear of 10 - 15 knots over 98L, and predicted the shear would remain in the moderate range through at least Wednesday. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 90% to 98L. Steering currents for 98L are very similar to what Danny experienced, and the 8 pm EDT (0Z) Monday run of the GFS and European models showed 98L taking a track into the northern Lesser Antilles Islands on Wednesday night, and into the Southeast Bahamas by Saturday. Wind shear will rise to a high 15 - 25 knots by Thursday as 98L brushes the Northeast Caribbean, which should slow development or cause weakening. A trough of low pressure capable of turning 98L to the north will set up shop along the U.S. East Coast late this week, but it is uncertain at this time whether or not 98L will be strong enough to get picked up by this trough. If so, 98L could represent a long-range threat to Bermuda or Canada next week. If not, then the Caribbean, Bahamas, and U.S. East Coast might be a target; it’s too early to narrow down the possibilities.

New tropical wave off of Africa little threat to develop
A strong tropical wave emerged from the coast of Africa on Sunday, and is headed west at 15 - 20 mph. The wave has warm ocean waters and moderate wind shear, but plenty of dry air from the Saharan Air Layer (SAL) is interfering with development. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odds of development of 10%.

Tropical Depression Kilo not expected to threaten Hawaii
Tropical Depression Kilo continues to mill around in the waters well west of the Hawaiian Islands, and is no longer expected to be a threat to Hawaii when the storm turns westwards away from Hawaii late this week. Outflow from Kilo brought plenty of dry, sinking air over Hawaii over the weekend, bringing sunny skies and record warm temperatures. This resulted in one of the highest temperatures ever recorded in Hawaii: a 97°F reading at Kahului on Maui Island on Saturday, August 22. According to wunderground weather historian Christopher C. Burt, this ties the all-time (for any month) high for Kahului measured on Aug. 31, 1994. According to weather records researcher Maximiliano Herrera, no other higher reliable temperatures have been measured in Hawaii (higher readings from an old station in Puunene, Maui in the 1950s are unreliable, and the Puunene station was closed in 1959.)

Hawaii should keep an eye on two tropical disturbances to its east, in the waters of the Eastern Pacific to the southwest of Mexico. Both of these disturbances (which were given 5-day development odds of 80% by NHC in their 8 am Monday Tropical Weather Outlook) could pose a long-range threat to Hawaii, according to the 6Z Monday run of the GFS model.

Typhoon Goni headed towards Japan
Category 3 Typhoon Goni is about to make landfall on the southern Japanese Island of Kyushu, with landfall as a Category 2 storm expected by the Joint Typhoon Warning Center.

Wunderblogger Steve Gregory has a post up today on 98L, and plans a more in-depth one late Monday afternoon.

WUTV Takes Over The Weather Channel Beginning at 6 pm EDT Monday
The Weather Underground hits live TV today, when the inaugural episode of the Weather Underground live cable TV show airs from 6-8 p.m. EDT Monday, August 24 on The Weather Channel (TWC). I’m in Atlanta today to help launch this unique effort, which aims appeal to everyone’s inner weather geek by focusing on the science behind weather and forecasting. Hosted by Emmy-award winning TWC meteorologist Mike Bettes, the show will air Monday through Friday from 6 - 8 pm Eastern time. I expect today we’ll be discussing Invest 98L and the rest of the action in the tropics. Check out #WUTV for updates.  

Jeff Masters