New tropical threats crossing the Atlantic
A slightly more active hurricane season than originally expected is now forecast, despite the predicted onset of an El Niño in the tropical Pacific Ocean.
The National Oceanic and Atmospheric Administration, the US body that operates the National Hurricane Center in Miami, increased the expected number range of named storms, hurricanes and major hurricanes in its annual mid-season update released Thursday.
“We are increasing the likelihood of an above-normal season because storm-conducive wind patterns and warmer-than-normal sea surface temperatures are now in place in the Atlantic,” said Gerry Bell, lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center. “These conditions are linked to the ongoing high activity era for Atlantic hurricanes that began in 1995. Also, strong early-season activity is generally indicative of a more active season.”
As it did in its pre-hurricane season forecast issued in late May, NOAA still forecasts a 50 per cent chance of a near-normal hurricane season, but increased the chances of an above-average season to 35 per cent, up 10 per cent from its May forecast.
El Niño is a cyclical anomalous warming of the sea surface temperatures in the equatorial Pacific Ocean.
Usually, when El Niño conditions appear, the anomaly inhibits tropical cyclone formation and strengthening. NOAA announced that an El Niño would likely develop in August or September.
Bell noted that the effects of the forming El Niño wouldn’t be seen immediately. “El Niño is a competing factor [in the Atlantic hurricane season], because it strengthens the vertical wind shear over the Atlantic, which suppresses storm development,” he said. “However, we don’t expect El Niño’s influence until later in the season.”
Klotzbach and Gray
Colorado State University scientists Phil Klotzbach and William Gray also increased the number of predicted tropical cyclones in their mid-season update issued last Friday, but they believe there will be slightly below average hurricane activity for the remainder of the season because of the weak El Niño.
Klotzbach and Gray now predict 14 named storms, six hurricanes and two major hurricanes. This represents a slight increase from their 1 June forecast of 13 named storms, five hurricanes and two major hurricanes.
Since Ernesto became a tropical storm and hurricane after their forecast last week, that would leave nine named storms, four hurricanes and two major hurricanes to go this year.
The duo noted that the late and weak onset of El Niño added uncertainty to their forecast.
“The [El Niño Southern Oscillation]-related warming trend in the tropical Pacific has slackened somewhat in recent weeks, and we are unsure as to how much impact El Niño will have on this year’s hurricane season,” the duo’s report stated. “The combination of the uncertainty in tropical Pacific conditions along with the low sea level pressure anomalies observed in recent weeks over the tropical Atlantic have led us to increase our forecast slightly.”
Although Tropical Storm Ernesto – which was downgraded from a hurricane after making landfall on the Yucatan Peninsula – was making a second landfall in Mexico Thursday and was expected to dissipate over land, the National Hurricane Center had identified two other areas of interest in the Atlantic Basin.
The first area of interest, the remnants of Tropical Storm Florence located north of the Leeward Islands, wasn’t expected to regenerate into a tropical cyclone. However, a second area associated with an area of low pressure located in the mid-tropical Atlantic was in environmental conditions that appeared conducive for further development and the National Hurricane Center gave the system a high 80 per cent chance of becoming a tropical cyclone by Saturday.
That system, which had been designated Invest 92L by the National Hurricane Center, could enter the Caribbean Sea late this weekend. As of Thursday afternoon, forecast models were split on whether the storm would continue moving westward in the Caribbean Sea or curve north before got there. However, the GFS model, which has done a good job with hurricane tracks this year and was particularly good with forecasting the track of Ernesto, forecast 92L to enter the Caribbean and then head slightly north in the general direction of the Cayman Islands. In addition, a tropical wave associated with a another area of low pressure just emerging off the west coast of Africa was given a 20 per cent chance of developing into a tropical cyclone by Saturday.