30 September 2013

What happened to hurricane season?

Tropical Storm Jerry has just formed in the central Atlantic, but like most storms this season, it would be easy to miss.  Today's post takes a look at the unexpectedly quiet hurricane season so far and can be found on the Capital Weather Gang blog:

What happened to hurricane season? And why we should keep forecasting it…

17 September 2013

Another Bay of Campeche storm in the making?

Since my last update on Sunday, Ingrid made landfall near La Pesca (Mexico) early Monday morning as expected, but weakened slightly and crossed the coastline as a tropical storm.  Of course, tropical storms are still capable of producing very heavy rain.  It continues to dissipate inland over mountainous areas of Mexico, but the flash flooding caused by both Ingrid (Mexico east coast) and Manuel (Mexico west coast) is responsible for at least 50 deaths now.

Humberto is back in the picture again... still in the central Atlantic and no threat to land.  It's located about 1000 miles WSW of the Azores and is a tropical storm with 45mph sustained winds.  Models and the NHC forecast it to become a sub-tropical cyclone shortly, then an extratropical cyclone or even open trough in a few days as it heads toward Iceland.

Visible satellite image of the Atlantic... with Tropical Storm Humberto on the far right, and the U.S. east coast on the far left.  For scale, Humberto is centered 2300 miles due east of Daytona Beach, FL.  (NOAA)
Now, on to the new disturbance, which once again is located near the Yucatan peninsula and headed for the Bay of Campeche.  If this sounds familiar, it should!  Back in May, Barbara snuck in from the eastern Pacific and then dissipated in the Bay of Campeche.  Other storms have since plagued the area, including Barry (June), Fernand (August), Tropical Depression 8 (September), and Ingrid (September).

Enhanced satellite image of the disturbance near Belize and the Yucatan peninsula. (NOAA)
In the near term, models agree on gradual development and a WNW track into the Bay of Campeche tomorrow.  Environmental conditions appear to be favorable (<10kts of shear, >29C SST, moist mid-levels, etc) for intensification in the foreseeable future, so this could easily become TD 11 then TS Jerry this week.

In the longer term (beyond 4-5 days), it's possible that this system will stall in the Gulf of Mexico and get picked up by a passing trough, which would allow for a track toward the northern Gulf coast.  This is a scenario that will be closely watched with each new set of model runs.  The alternative would be a track very similar to Ingrid's.

15 September 2013

Hurricane Ingrid to hit Mexico tonight

Ingrid did what so  many storms in the Bay of Campeche do: intensify really fast in a small amount of space.

In the past 24 hours (09Z yesterday - 09Z today), the central pressure fell just 5mb, but the winds increased by 25kts.  Further intensification is expected, perhaps reaching Category 2 status at landfall overnight.  One key factor in limiting really rapid intensification is actually another tropical cyclone!  Tropical Storm Manuel is on the other side of Mexico and the upper-level circulation over each cyclone is producing wind shear over the other.

Tropical Storm Manuel in the East Pacific, and Hurricane Ingrid in the Gulf of Mexico are "attacking" Mexico from both sides today.  (CIRA/RAMMB)
Ingrid is located about 150 miles east of Tampico, and tracking northwest at 7mph.  Maximum winds are 85mph and it is expected to make landfall .  Again, rainfall will be a major concern, with 1-2 feet forecast over a fairly large area.  Along the coast and to the north of where it makes landfall, a 3-5 foot storm surge is expected as well.  Extreme south Texas could also get several inches of rain from Ingrid in the coming days.

Unfortunately, radar coverage of landfall is hindered due to technical problems with the radar in Altamira, Mexico.  The radars in Alvarado, Mexico and Brownsville, Texas are too far away.  However, there are a variety of satellite loops available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/atlantic/

Elsewhere, Humberto has temporarily weakened below Depression status, but is being watched for likely regeneration... still in the middle of the Atlantic.

12 September 2013

TD10 forming in Bay of Campeche, Gabrielle and Humberto update

All signs point to Tropical Depression 10 forming in the Bay of Campeche this afternoon.  The disturbance that I mentioned in Tuesday's update has crossed the Yucatan peninsula and is now back over water.  As the models predicted, it is taking shape and getting better organized.

Afternoon visible satellite image over the southern Gulf of Mexico.  (CIRA/RAMMB)
As I write this, an aircraft is en route to reconnoiter the developing storm, but earlier today, a satellite that measures surface wind speeds passed over the area and observed what certainly looks like a closed circulation to me.

Surface winds as seen from the ASCAT instrument at 12:25pm EDT today showing a circulation centered in the middle of the Bay of Campeche.  (OSI SAF)
I also have radar loops available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/ where you can monitor the progress of the storm when it's close to the coast.  The loop from Sabancuy started at 7am EDT today and shows it leaving the peninsula.  The loop from Alvarado will be handy in the coming days.

The model guidance remains in agreement on the track and intensity (in general).  While there are some differences, the system is expected to move quite slowly to the W or WNW toward Mexico, and intensify.  At the moment, the strongest it is forecast to get is a minimal hurricane, but most models keep it at tropical storm intensity with a landfall sometime early next week.

The next name on the list is Ingrid.


Gabrielle weakened to a Depression when it was at its closest approach to Bermuda, but has since re-intensified to a Tropical Storm.  It's now about 200 miles NW of Bermuda, but this last gasp will be short-lived.  Environmental conditions will soon become too hostile and it will dissipate as it heads toward an encounter with Nova Scotia on Friday evening.

Enhanced satellite image of Tropical Storm Gabrielle on Thursday afternoon.  The strong thunderstorms (white) are far displaced from the surface circulation (yellow).  Bermuda is southeast of the storm. (NOAA)

Humberto has now been a hurricane for nearly two days, and it might have one more day to go before it weakens.  It is located about 460 miles northwest of the northernmost of the Cape Verde islands.  The figure below shows the past track in gray, the current location as a red hurricane symbol, and various model forecast tracks in colored lines.

11 September 2013

Humberto becomes first hurricane of the season

Within hours of breaking the record for latest date of first hurricane formation, Humberto was upgraded to a hurricane at 5am EDT today based on its satellite presentation.  The record holder is still Gustav, which became a hurricane at 8am EDT on September 11, 2002.
 (Note that operationally, advisories come out at 5am, 11am, 5pm, 11pm EDT (09Z, 15Z, 21Z, 03Z), while in the "best track" database, values are recorded at 2am, 8am, 2pm, 8pm EDT (06Z, 12Z, 18Z, 00Z).

So, Gustav (2002) and Humberto (2013) will have to share Sep 11th, then Diana (1984) has Sep 10th, then Erin (2001) has Sep 9th.

This morning, Humberto remains a minimal hurricane and is located about 300 miles west of the Cape Verde islands.

The track forecast remains the same... head north for a couple days then make a sharp turn to the west when it encounters a strong subtropical ridge.  By that time, the wind shear is expected to be quite strong, so it's forecast to weaken back to a tropical storm.  The image below is zoomed out quite far to give you a perspective of where it is and where it's going.  The last "S" marker is the NHC forecast position on Monday.

The disturbance near the Yucatan peninsula has indeed continued to develop, and is now consolidating near the Mexico/Belize border.  The central pressure is down to 1009mb, and though it will likely lose some of its organization as it crosses the peninsula, it is expected to make a quick comeback once it hits the Bay of Campeche tomorrow morning.

Infrared satellite image of the disturbance heading into the Yucatan peninsula.  The bright colors indicate very cold, high cloud tops found over intense thunderstorms.  (CIRA/RAMMB)
Model track guidance is keeping the future storm further south, making the southern Texas option less likely.  As far as intensity goes, models top out at a strong tropical storm, so it's not a huge concern... just heavy rain for Mexico, but the same part of Mexico that already got hit by TS Barry, TS Fernand, and TD 8 this year.  More on this tomorrow once we see how it fares crossing land.  If it becomes a tropical storm, the next name is Ingrid.

As expected, Gabrielle is losing its punch as it heads into cooler waters and higher shear.  As of this morning, it's just a skeletal cyclone; all that remains of it is a low-level cloud swirl.  Maximum sustained winds are 50mph according to the 5am EDT advisory, and it is centered just a few miles west of Bermuda (the magenta mark in the image below).  It is still expected to reach Nova Scotia by Friday night, probably not as a tropical entity though.

Enhanced satellite image of Gabrielle passing by Bermuda on Wednesday morning.  Low clouds show up as yellow, while high clouds show up as white.  (NOAA)

09 September 2013

Humberto forms, could become season's first hurricane

This week is the climatological peak of the Atlantic hurricane season, but this year, it arrives with little fanfare.  Though there has not been a single hurricane yet, that could change very soon.

On Sunday evening, Tropical Depression 9 formed just off the African coast from a potent easterly wave.   This morning, it was upgraded to Tropical Storm Humberto, the ninth named storm of the season.  It is presently centered just south of the Cape Verde islands and tracking west at 12mph.

Enhanced infrared satellite image of Humberto at 8:30am EDT this morning.  (CIRA/RAMMB)
It is forecast to become a hurricane by Wednesday.  If you recall, the latest date of first hurricane formation in the aircraft reconnaissance and satellite era (back to 1944) is September 11, and that record was set back in 2002.  Specifically, it was 1200 UTC on September 11, and when it comes to the record, hours might count.  The 5am EDT forecast from NHC today brings Humberto to hurricane intensity at 0600 UTC (2am EDT) on the 11th.  But based on current appearance and trends, I'd suspect that the timeframe will be nudged forward/sooner.

Since 1851, 34 storms formed or passed within 100 miles of where Humberto did (18 of which were in September).  As you can see below, the tracks of these storms have large variability, ranging from a quick recurvature to long-tracked major hurricanes that plow into the U.S.  The current official forecast track for Humberto would be the quickest and furthest east recurvature off all of these.

Past tracks of all known storms that formed or passed within 100mi of where Humberto formed.
Models are in fairly good agreement on the quick recurvature scenario too, so the odds of it becoming a threat to land are extremely small.

Select model forecasts as well as the NHC forecast for Humberto, from the 0600 UTC runs today. (NCAR)
The name Humberto has been in the rotation since 1995 (that is, it has been used in 1995, 2001, 2007, and 2013).  It replaced Hugo, which was retired in 1989 after its devastating landfall on South Carolina on September 22 of that year.  In all likelihood, it will stick around for another reincarnation in 2019!

Elsewhere, the remnants of Gabrielle are still hanging around between Bermuda and Hispaniola.  The environment is likely going to remain too hostile for any tropical redevelopment, but it could become a stronger subtropical or extratropical cyclone and potentially impact, Bermuda, Newfoundland, or Nova Scotia.

07 September 2013

Gabrielle, TD8, and eastern Atlantic disturbance

Since my last update on Thursday, Tropical Storm Gabrielle dissipated due to a combination of shear, dry air, and land interaction with Puerto Rico.  However, the remnants are still very much trackable, and are showing signs of regeneration now that the system is north of Puerto Rico and Hispaniola.

Enhanced satellite image of former Gabrielle.  The center (marked with a red L) is nearly exposed on the northwest side of the deep convection.  The sharp boundary of the high clouds there is indicative of strong vertical shear.  (NOAA)
Though over very warm water (29C), the vertical wind shear is up near 30kts and is not expected to relax in the foreseeable future.  That will be the primary factor in inhibiting its regeneration.  NHC is giving it a 40% chance of formation over the next 5 days, and I would agree with that number... IF it reforms, it would be working against the odds.

The track guidance is all over the place, largely due to the uncertainty in whether or not it regains some sort of organization.  Not all models agree on that, so of course, not all models agree on a similar track. 

Moving on to TD8... if you sneezed, you missed it.  It formed yesterday afternoon in the extreme southwestern Gulf of Mexico, right on the coastline, and then dissipated inland early this morning.  It was never named -- just a short-lived Tropical Depression.

Elsewhere, there is a strong easterly wave located approximately 700 miles west of the Cape Verde islands.  It exited the African coast back on Sept 2.  As you can see below, it's not very well organized at all yet.

Most models bring it N-NW for another day or so, then flatten out to a more W course for several days.  Even in five days, it will still be short of the Lesser Antilles, so there is time to see how this one evolves.  I'll add additional details in a future post, but for now, it's at least worth pointing out.

01 September 2013

Disturbance heading into eastern Caribbean

An easterly wave that left the African coast about a week ago is just about to cross the Lesser Antilles and enter the eastern Caribbean.  It has been inactive for most of the journey, but has gained organization and persistent deep convection over the past 24 hours.

Enhanced satellite image over the Lesser Antilles on Sunday afternoon.  (NOAA)
The environmental conditions are presently conducive for further development, and are expected to remain so for at least the coming week.  It is in 5-10 kts of vertical shear, over 29C sea surface temperatures, and the mid-level humidity is high enough to support growth.  You can view a radar loop of it as it passes through the islands here (new frames continuously added, so check back later too).

Forecasts of intensity, track, shear, SST, and mid-level humidity from a small selection of models.
So, we will clearly have to watch this closely, as model solutions range from near-nothing to a Category 3 hurricane in 5 days near Jamaica.  Right now, it's too soon to get concerned, but not too soon to pay attention.  HWRF, the model solution in blue on the plot above, is interesting because it has the storm becoming a minimal hurricane by mid-week, then weakening slightly as it crosses Haiti and eastern Cuba, then picking back up with a possible track toward south Florida next weekend.

5-day forecast from an HWRF run today... valid Friday afternoon.  The colored contours are surface wind and the black line contours are surface pressure.