Valid September 20, 2017 at 8:00 PM CT
Note: Last week’s tropical blog was the first posted in a public forum to Weather Unlimited. That practice shall continue this week. However, there are improvements planned to the blog, including better connections between the various ingredients and factors that play into the tropical cyclones.
Barely weeks after Hurricane Irma knocked out power and brought damage to the Virgin Islands and Puerto Rico, yet another major hurricane is wreaking havoc on the islands. Hurricane Maria made landfall on Wednesday over Puerto Rico as a strong category 4 hurricane, knocking out power to the entire island. As of the 8:00 pm AST advisory, Maria has weakened to a category 2 storm with 110 mph sustained winds, re-emerging into the Atlantic off the northwest coast of Puerto Rico.
Figure 1 – The National Hurricane Center 8:00 pm AST advisory for Hurricane Maria, which has returned to the Atlantic Ocean.
The future for Maria would suggest some strengthening possible before reaching north of the Bahamas. The general steering flow for this hurricane, located between 300 and 850 millibars due to its current strength, shows mostly weak flow leading up towards the Bahamas. However, the steering flow strengthens once north of the islands, suggesting a stronger turn out to sea possible.
Figure 2 – The general steering flow of the western Atlantic Ocean, as governed by the 300 to 850 millibar average winds.
While Maria will not encounter a stronger steering flow until it passes north of the Bahamas in all likelihood, it will likely encounter stronger shear earlier. Areas of favorable shear remain just to the north of Puerto Rico and Hispaniola, but do not extend further east of the Turks and Caicos Islands. This will likely cap any further strengthening by Maria, or lead to weakening before it comes close to the United States. The shear tendency also suggests increasing unfavorable shear levels north of Puerto Rico and the Dominican Republic, furthering the argument that any re-strengthening by Maria would be limited. As a Category 2 storm now, it would be likely that Maria would be unable to reach Category 4 or 5 strength again.
Figure 3 – Vertical wind shear (top) and shear tendency (bottom) for the western Atlantic Ocean, showing that Maria will be working into areas of less favorable development.
While shear and shear tendency would appear to suggest continued weakening by Maria, combining a weak steering flow with still anomalously warm sea surface temperatures will help Maria regain some of its strength. The warm ocean waters will continue to fuel Maria, and could help the storm regain major hurricane status.
Figure 4 – Sea surface temperatures (top) and sea surface temperature anomalies (bottom) show that Maria will still have warm ocean waters to pull energy from.
Interestingly, the model guidance from the GFS and ECMWF disagree with the idea of Maria not strengthening significantly. Both bring Maria close to the Bahamas as a hurricane with a minimum central pressure of at least 943 millibars, with the GFS going even lower to 929 millibars. These models also do not recurve the storm as intensely as the steering flow out ahead of Maria would suggest. Instead, both models keep the storm closer to the U.S. coastline, especially the ECMWF.
Figure 5 – Global model guidance from the ECMWF (top) and GFS (bottom) does agree with the assumptions made based on the ingredients in the tropics, instead suggesting Maria will strengthen significantly.
In terms of future tropical development, just two potential lows could further develop into a significant tropical disturbance. The low centered over the open eastern Atlantic is the remnants of Tropical Storm Lee, and the National Hurricane Center does not expect much development in the next few days. Much of the typical tropical ingredients would agree with this assessment. While sea surface temperatures remain warm, the convection associated with the system is very disorganized. The only other area worth watching is a wave over west Africa, which should emerge over the Atlantic in the coming days.
Figure 6 – The latest surface map shows the location of Hurricane Maria (near center), and the areas of future potential development (right of Maria).
Other Tropical Tidbits
Tropical Storm Jose is expected to meander near the New England coast for at least four to five days, bringing more rain to Cape Cod and Nantucket. An area of potential development has been identified in the Eastern Pacific, with a 50 percent chance of development in the next 48 hours. There is also an area with a slight chance of development in the Central Pacific. The Western Pacific is quiet for now.
Meanwhile, back in the United States, the cleanup continues from Harvey and Irma. Two racetracks in Texas have been converted into car graveyards. In Florida, officials fear damage to the orange crop could be the death nail for orange juice.
The tropical update blog is part of a weekly assignment for Dr. Kim Wood’s Tropical Meteorology class at Mississippi State University. Post created for academic purposes.