GULF OF MEXICO LOW PRESSURE SYSTEM FORECAST SYNOPSIS…ISSUED APR. 10, 2023…8:55 P.M. EDT6 min read
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(T. F. “Storm” Walsh)
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I will reiterate, my forecasts are based on the available information at the time of analysis, and are only as accurate as the information analyzed and the solutions provided.
Good evening everyone!
It was my intention to update on the evening of Easter Sunday, however while attending a a party outdoors on Sat. evening, my wife tripped and fell due to a hidden tree root, thin like wire, and sustained soft tissue damage to her right shoulder. Long story short, I wound up helping her bring items in from our aster celebration, and cleaning up in the kitchen until late.
Analysis this evening of the various global models still indicate an area of low pressure to develop IVO the central GOMEX. While modeling indicates this to initiate by Wed., the current Tropical Weather Discussion from the NHC indicates the low should initialize sometime tomorrow. From the NHC:
A stationary front stretches from Key West, FL, to the central Gulf near 24N88W. Scattered showers and thunderstorms continue along this boundary. Recent buoy observations recorded fresh to strong NE winds in the NE Gulf, where seas are 5 to 7 ft. Moderate to fresh NE winds are elsewhere behind the front, with 5 to 6 ft seas. South of 24N, gentle to moderate E-NE winds prevail with 2 to 4 ft seas. For the forecast, fresh to strong easterly winds with higher seas behind the front will persist across the northeastern and east-central Gulf and near the Florida Keys through Thu. A modest low pressure system is expected to develop near the western end of the stationary front on Tue. It should lift northward while becoming better organized through Thu, and then move inland over southern Louisiana on Thu night or Fri morning. In response, fresh to strong ENE to ESE winds and rising seas are expected at the north-central Gulf Tue through Thu.
Development should occur near or just north of the circled area. The direction in which way the frontal symbols are facing, depict the motion of that portion of the frontal boundary. In other words, the warm front symbol is moving toward the north, and cold front symbol moving south. So, there you have rotation.
TAFB 12Z SURFACE ANALYSIS (CLICK TO ZOOM)
The various global models indicate different takes on strength, however it appears this low will remain around 1005 – 1012 mb at the moment. Of course we’ll have to see what real time brings.
Even though waters in the GOMEX are warm enough to sustain a sub-tropical system, the same negating factors still exist as mentioned in my initial forecast a few days ago. Strong wind shear is forecast to be in place, with zonal winds at the 200 mb level meaning there will be no outflow aloft to evacuate winds aloft. Winds aloft must be in a diffluent to divergent pattern to allow for outflow in order to allow for air and heat to converge at the sea surface.
WIND SHEAR FORECAST
200 MB WIND FORECAST
Another negating factor is going to be the lack of sufficient moisture in the atmosphere. Dry air is going to be present at the mid levels (500 mb), while precipitable water is almost negligible. What I look for in RH, is around 60 – 65% at a minimum for a tropical system, and high values of precipitable water.
RELATIVE HUMIDITY FORECAST
Analysis of the various global models also determines this system is forecast to remain “cold core”, based on analysis of forecast thermal winds. In order for a system to become subtropical or tropical, the “center” of the cyclone must become a warm core system. An excerpt from a Wikipedia article:
Most subtropical cyclones form when a deep cold-core extratropical cyclone drops down into the subtropics. The system becomes blocked by a high latitude ridge, and eventually sheds its frontal boundaries as its source of cool and dry air from the high latitudes diverts away from the system, and warms the central circulation, allowing further transition. Temperature differences between the 500 hPa pressure level and the sea surface temperatures initially exceed the dry adiabatic lapse rate, which causes an initial round of thunderstorms to form at a distance east of the center. Due to the initial cold temperatures aloft, sea surface temperatures usually need to reach at least 20 °C (68 °F) for this initial round of thunderstorms. The initial thunderstorm activity humidifies the environment around the low pressure system, which destabilizes the atmosphere by reducing the lapse rate needed for convection. When the next shortwave or upper level jet streak (wind maximum within the jet stream) moves nearby, the convection reignites closer to the center, which warms the core and develops the system into a true subtropical cyclone. The average sea surface temperature that helps lead to subtropical cyclogenesis is 24 °C (75 °F). If the thunderstorm activity becomes deep and persistent, allowing its initial low level warm core to deepen, extension to tropical cyclogenesis is possible.
THERMAL WINDS FORECAST
Lower Troposphere Thermal Wind Vs Lower Troposphere Frontal Nature
Lower Troposphere Thermal Wind Vs Upper Troposphere Thermal Wind
Based on the analysis of all these factors, I do not expect at the moment for this to become sub-tropical. The ECMWF EPS Cyclone Probability forecast does not indicate any tropical development, and this should resemble more of a mid latitude cyclone.
Residents in areas over lower portions of Louisiana and Mississippi may experience localized heavy rainfall. Wave heights along the coastal areas could reach between 8 – 10 ft.
WPC 7 DAY RAINFALL FORECAST
ECMWF WAVE HEIGHTS FORECAST
I will continue to monitor this area over the next 48 hours, and intend to update as time permits. Hopefully on the next update, we will have something to see on satellite.
You may direct any questions by contacting me personally, ANYTIME, at: firstname.lastname@example.org
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
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